Spreadsheet editor always creates an error "Internet connection has been restored"

[arnowelzel]

I also explained this in #369 but it makes more sense to have a separate ticket for this as this happens with the offcial Docker version by ONLYOFFICE.

Server: ONLYOFFICE Docker version 5.6.5 (but this also happens with 5.6.4 and 5.6.0 and also when running ONLYOFFICE installed on Debian 10 via apt as described in https://helpcenter.onlyoffice.com/de/server/linux/document/linux-installation.aspx)
Nextcloud version: 19.0.3
Integration app: 6.0.0

Steps to reproduce:

1. Create a new spreadsheet in Nextcloud

2. Open it with the integration app and start editing

3. After a while you will see the following error message: "Internet connection has been restored, and the file version has been changed. Before you can continue working, you need to download the file or copy its content to make sure nothing is lost, and then reload the page." - also see the screenshot:
   

When this happens, the following error is found in the log file /var/log/onlyoffice/documentserver/docservice:

[2020-09-26T14:27:39.932] [WARN] nodeJS - error description: docId = 3739872172 errorId = Update Version error

At the time when this happens, I was the only user working with that file and I was connected to the server through a stable connection.

What can cause an "Update Version error"?

[arnowelzel]

The problem is solved - it was caused by a server misconfiguration in the Apache proxy :-(

Hint: never use ProxyTimeout!