A couple of issues.

[LordBalthazar]

I currently have my echo set up with routines for each room of my house. I have several different routines for most of the rooms. Two routines that seem to be hit-or-miss are my "Dim the Livingroom Lights" and "Turn off nursery light". These routines will work for a while but then they will seem to "break". The routine to dim the living room lights will tell me "I don't know how to set Living room 2 to that setting" (there are 3 bulbs) which is the same setting as the other two bulbs (see screen shot: https://drive.google.com/file/d/0Bxk5_3xOkVjeM1MxWXNBR0VZTnhlaEQ0YlBFM2NhOUh6TGdF/view?usp=sharing). The error is always with Bulb 2, and there doesn't seem to be issues with any of the other routines that control that bulb. I have a routine called "movie mode" which turns off bulbs 1 & 2 and dims bulb 3 to 10%. I have never had an issue with this routine.

The other one is the nursery. The command for this was originally "Turn off Kristi's light" (as my daughter's name is Kristiana). But it kept telling me it couldn't find a device called "Kristi's light". I then changed the command replacing "Kristi's" with "nursery" and it worked for about a day then it too started saying "I can't find a device called "nursery light". I have this routine set up exactly like all of the other routines, the only difference is there's only 1 bulb in her light (the bulb's name is "Kristiana's Room"), whereas all the other routines manage multiple bulbs. But I really can't see this being the issue. Also, if I tap the "play" icon next to the routine, it will work fine. (see screen shot of routine: https://drive.google.com/file/d/0Bxk5_3xOkVjeLTlpcmhJbzNFaE5xaGhFOUlTaDZJUldZQURn/view?usp=sharing)

Any thoughts?

[kenf]

Do you have any overlap in names?  A recent change in ALexa made my house have some issues with finding devices by name when the was overlap.

I'll give an example.  In my living room, unlike the rest of my rooms, I have 3 smart switches.  To maintain my sanity (a year ago when I named them), they all start with "Living Room".  Giving me a list of names for:
Living Room (Echo)
Living Room (group)
Living Room Light
Living Room Lamp
Reading Lamp

The last one broke the pattern as I couldn't think of anything else.  With that recent fw update, I started getting failure to find devices by name.

The recommendation is to make the names NOT start with the same word to get around the problem with the voice recognition.  Unlike a 3-year old, instead of only hearing the last thing I said, she hears the first part "living room" then drifts off, thus garbling and getting confused on what I wanted.

In your case, things are different.  Try some science. The names of devices inside the routine should not matter, directly.  Alexa isn't calling them by name, she should be using their magic ID# the programmers established for that device entry.

So, as it related to my example, your first risk is whether your Routine name is too close to the name of a device.  For the moment, rename your Routine to be "Bob" so you can say "Alexa, Bob" to start it.

If that works (consistently) then the issue was your routine name was too close to the lights ' names and Alexa got confused.

If it still fails, then the other issue is the light/switch is flakey and isn't receiving commands reliably.  Thus Alexa is confused about the device definition (knowing it is dimmable) or it isn't responding with an ACK signal after the command is sent.

This would be an issue with the smart bulb itself, the cloud service (ex. Hue) that these devices actually talk to and Alexa sends commands to Hue's cloud which in turn sends a command to your Hue Hub which sends a command to the bulb.  Any interference in the chain could cause a device not to respond.

So, the extra questions are:
what brand of Smart Bulb are you using?
How far is the bulb in question from the Hub or Wi-Fi router?
Are there sources of interference nearby (like Flourescent lights)?
Does it work if you use the vendor's app directly to that bulb?
Does the problem move if your swap bulb positions?
Do you own your residence and like doing electrical work (consider smart switches instead)?

[LordBalthazar]

Do you have any overlap in names? 

I believe so. My bulb names are:
Living Room 1
Living Room 2
Living Room 3
Master Bedroom 1
Master Bedroom 2
Master Bedroom 3
Master Bedroom 4
Kristiana's Room
(I haven't yet bought bulbs for our kitchen)

My Echos are named:
Master Bedroom Dot
Kitchen Dot
Livingroom Echo
Kristi's Dot

As for my routines, most of them start with "Turn off/Turn on" and then the room name.

If it still fails, then the other issue is the light/switch is flakey and isn't receiving commands reliably.  Thus Alexa is confused about the device definition (knowing it is dimmable) or it isn't responding with an ACK signal after the command is sent.

This would be an issue with the smart bulb itself, the cloud service (ex. Hue) that these devices actually talk to and Alexa sends commands to Hue's cloud which in turn sends a command to your Hue Hub which sends a command to the bulb.  Any interference in the chain could cause a device not to respond.

Is the process different if I tap the "play" button next to the routine? Cause even if it tells me it can't find the bulb with voice commands, if I tap the play button it will work.

So, the extra questions are:
what brand of Smart Bulb are you using?
How far is the bulb in question from the Hub or Wi-Fi router?
Are there sources of interference nearby (like Flourescent lights)?
Does it work if you use the vendor's app directly to that bulb?
Does the problem move if your swap bulb positions?
Do you own your residence and like doing electrical work (consider smart switches instead)?

1. Eufy (https://www.eufylife.com/) Not the highest quality, but works well for the money and doesn't require a HUB.
2. The nursery light is probably 15-20 feet from the router, the living room light is probably 30-40 feet.
3. As far as I know there are no sources of interference. We don't have any fluorescent lights. The only thing that could possibly cause it (and I highly doubt it) is our TV which our living room echo sits next to (mainly to keep it away from the baby)
4. Yes, flawlessly
5. I'm not sure what you mean by this. I'm guessing you mean moving the bulbs from one room to another to see if there is still a problem. I haven't tried this yet, however.
6. Smart Switches is a possibility for the future. However I have all these bulbs for right now, and 95% of the time they work. Plus, there are certain commands that I haven't had a problem with, which is what makes this even more confusing.

[renegade600]

might want to spell out the numbers.  alexa does get numbers confused.  in the routine names, example, try master bedroom off, master bedroom on.  Using turn on/off could be confusing for alexa since that is the command for turning on/off single devices. 

[kenf]

for number 5, that's exactly what I meant.  swap the problem bulb with a good bulb and see if the bad behavior follows the bulb or stays at the fixture position.

As the topic came up elsewhere, individual wifi devices take up slots on your router.  Long term, I am not a fan of smart bulbs or hub-less wifi devices for smart home.  But this is what you got.

If the vendor app works flawlessly, that means the signal from router to bulbs is reasonably good. The problem is likely in Alexa confusing the names or relaying the signal to the bulbs (probably indirectly via vendor's cloud).

I'm not a fan of you using Routines to do what Groups are for.  Your question came up at the right time on the SmartThings forum.  See what's been said about it over there (it's a Samsung SmartThings forum, but this thread is almost entirely about Alexa Groups and naming)
https://community.smartthings.com/t/best-way-to-name-devices-in-regards-to-alexa-2018/138257/11

Try disabling the routine for the problem room and doing a Group instead.  Use Routines for the last mile, that which Groups don't solve.

[LordBalthazar]

might want to spell out the numbers.  alexa does get numbers confused.  in the routine names, example, try master bedroom off, master bedroom on.  Using turn on/off could be confusing for alexa since that is the command for turning on/off single devices.

Thanks, I'll try that.

I'm not a fan of you using Routines to do what Groups are for.  Your question came up at the right time on the SmartThings forum.  See what's been said about it over there (it's a Samsung SmartThings forum, but this thread is almost entirely about Alexa Groups and naming)
https://community.smartthings.com/t/best-way-to-name-devices-in-regards-to-alexa-2018/138257/11

Try disabling the routine for the problem room and doing a Group instead.  Use Routines for the last mile, that which Groups don't solve.

I did make a group for each room and it seems to be working better. However there seems to be a really bad delay in my kitchen. But I'm guessing that's because Alexa has to relay the command through my wifi extender to my router and back to the bulb.

Incidenly I am about to order a Samsung SmartThings hub at the end of this month. We have decided to take the automation a bit further and buy a smart lock for our door because my wife is always questioning if she locked the door. It requires a hub and the recommended hub for it is the SmartThings.