First, the unified view is just that, a view. The actual Gmail inbox is what is being acted up. For the phone to be in sync, both need to be set up as IMAP accounts. If unsure, highlight account name on main view, rightclick and select settings, then click 'server settings' and the type (IMAP or POP) will be displayed. Also, you cannot change an account from one to the other, but must set up a new account.

That's what I was expecting ...  ;)

Both accounts are IMAP.

everything is usually synced - except these deletions (I am new to thunderbird).

Check your account online and compare to what your phone is showing. That may guide you to wherever the problem lies .

The mails are also undeleted in the original Gmail account online.

in that case, i suggest reviewing the server settings on disposition of deleted messages. There may also be settings in the online Gmail settings.

I deselected "Archive messages" and now it's working great.

I'm glad it's resolved. :)

Thank you for the super quick help!

) Youre welcome.