1:1 Teams Chat between commercial and DOD - 504 error

Hi.  Wondering if anyone can tell me what setting I ought to look for to figure out what happened.  I used to be able to chat 1:1 with government from commercial and DoD via skype interop.  I went through a domain change, and now when I try to chat, I get "message failed to send" or I get a 504/1008 error.  

Doesn't make sense to me.  

Would appreciate any guidance/help on what to look for.

Microsoft support hasn't been helpful.  Almost all public documentation says, "turn on cross cloud".  But that's not so much the issue.