Chat fails after account reset

I had an account reset a week ago. Since then I can't chat to certain people. Opening the chat results in an error message:

"There was an error creating the coversation. You are not a member of this team."

Start by reproducing the chat-opening flow after an account reset, focusing on conversations where the user is reported as not being a team member. Trace the source of the error message and verify the behavior for affected and unaffected contacts; done means eligible chats open without the membership error.

Written by the indexing model from the issue text.