I have something similar set up with my Ring doorbell and a couple of outside lights. My outside lightbulbs are the color smart bulbs made by Feit - got them from Costco when they were on sale 4 for $20. They work perfectly, never any problems.
My guess your Wifi signal outside your garage is probably spotty. If the bulbs are working fine when you control them via the Alexa app, it is likely the app is looking for the bulbs to get its current status when you are on the devices and groups screen. That establishes a connection to your bulbs. So when you turn on/off the bulbs or run the routine manually it seems to work fine. However, during a normal triggered routine, the connection is not established ahead of time. Alexa will send the command to Meross and moves on to the next step. If Wifi issues prevent the initial power on command, then it is just skipped. As a workaround, you could make your routine to turn on the bulb twice. In the actions, turn on the bulb, wait 5 seconds, then turn on the bulb again. So if it missed the first power on command, it should power on with the second command.