We are having the same problem, our reverse proxy is oracle HTTP server (essentially apache). We are using a virtual path from https - our document server is running as a docker container:
Any ideas what could be the problem here (we have had the issue for quite some time so have not upgraded our environment due to this issue so are running 7.2.1 in production).
Revert to classic socket.io upgrade to fix connection issue with proxy
I believe you can update your installation to the latest version (v.8.0.1) without mentioned issue. However, we strongly recommend preparing whole server backup before update process just in case.
The another way, please try to deploy the latest version of Docs on a separate server with your proxy server to check it out.
Here’re our actual proxy samples, I believe they will be useful: Using ONLYOFFICE Docs behind the proxy - ONLYOFFICE