Not sure if this helps.
I have multiple echo devices around my house on different Amazon accounts.
Account 1: I have a "Show", "Dot", "Wand"
Account 2: "2 * Dots"
Using the same app on my phone logging in on different accounts.
Account 1: I see the icon and can use Drop In etc
Account 2: I can;t see the icon.
I don't think it's app specific it must be something else. It is doing my head in trying to figure it out.
I am using from Australia so not sure if it has to do with where the account was created? Account 1 was created years a go. The others are only new.
SOLVED MY OWN ISSUE: Hope this helps someone else.
MY assumptions/solution
I found that if I created an Amazon account separate to the one that purchased the device from the Alexa app it did not link this account to a physical location. As some of the features are geo based and it did not have an address associated with the account some features were missing.
If I logged into the Amazon account
www.amazon.com added a US based address to the account "Manage Your Content and Devices" Section. Not a postal address. When I logged back into the Alexa app the conversation icon appeared.
Hope this helps someone else.