I don't know if this is it, but in the Work Environment > More Options, there is an option to "Show New Message Alert in Teamwork".
Updating will not usually change WE settings though.
Barry.
One of the forum moderators. Versions 6.5 to 27 i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10 Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11
I suggest to repair Archicad and try again - we have no other reported cases at the moment, so I hope that repairing all services / preferences files can solve your issue.