Rocketchat Client in EGw, Getting setup instead of messages

[AlexS]

Hello Together,
yesterday I moved EGroupware again to a new BOX. It is still running EGw 19.1. Rocketchat is version 3.5.2. I moved also the rocketchat mongo database via mongodump and mongorestore. Now I can access rc via https:/myserver/rocketchat without any problems, but when I try to access it from inside EGw I get step 1 of the setup wizard:

I don’t see anything In the logs (rocketchat, egroupware, console).
What can I do?
Thank you for your support and best regads
Alex

[AlexS]

Hello Again,
following my previous message I noticed that this only happens o Firefox:

Chrome seems to be working fine.
Greetings
Alex

[AlexS]

In Firefox Version 80.0.1 the issue is gone…
BR
Alex