So that would mean that if Coinos included the lud16 in their connect string Damus would use the associated Coinos LN address to receive instead of whatever LN address was set in the profile?

OK, so I looked at the Coinos connect string and it does include the lud16. That means the Damus is using that instead of the defined LN address from the profile (the Cashu address). If we manually add the Cashu lud16 to the Cashu connect string and paste that into Damus, it should work properly then, correct? Because that makes a lot of sense based on what you've said.

I'm going to have him do that and we'll see if the problem goes away. Thank you very much for taking the time to help with this problem. I appreciate your expertise and assistance.