Collabora Office -> Socket connection could not be established or Socket connection closed unexpectedly. The reverse proxy may be misconfigured

[Octopus2]

I have a problem in Nextcloud version 31.0.2 and a server at Hetzner that I set up with the script.

In my home network with the PC but also from my mobile phone, I can edit documents directly in the browser with Collabora Office without any problems.

At my workplace in a larger network, however, the following error message appears when opening Collabora Office:

Loading the document failed
Socket connection could not be established or Socket connection closed unexpectedly. The reverse proxy may be misconfigured. Please contact your administrator. For more information on proxy configuration, see https://sdk.collaboraonline.com/docs/installation/Proxy_settings.html

Does anyone have any ideas on how I can get around this? Of course, I can't change the network at work....