When it happens to me, I click on the link (the one with the arrow), and the web version of Nextcloud opens in the browser.
From there, after 30 seconds the Nextcloud client “awakes”, connect and starts to synchronize.
And all works fine until my computer suspends, shuts down or restarts.
When I turn the computer back on, I have to do the same operation, otherwise hours go by without the client being able to synchronize.
I tried to change my client to another version (since yesterdeay, I had 3.3.6 and now I tried 3.6.4 and others…), but it happends the same.
I have the last versions of syncloud: System:1760 - Installer:312, and Nextcloud: Version: 660 - 25.0.2
All I see is this in the log, and this was happening because we had issues with our dns service and it was finally fixed yesterday late evening after this log. Was happening for few days and potentially for weeks.
This should not have caused any app issues unless your device changes its IP move than one time a day.
2023-01-27 16:28:27,280 - util - ERROR - <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<title>502 Proxy Error</title>
<p>The proxy server received an invalid
response from an upstream server.<br />
The proxy server could not handle the request<p>Reason: <strong>Error reading from remote server</strong></p></p>
<address>Apache/2.4.18 (Ubuntu) Server at api.syncloud.it Port 443</address>
Could you send logs one more time right after this happens again please?
It is possible that 500 is actually coming from another server every time your device changes IP windows does not update dns quick enough. If that is the case then maybe DNS server you use in your network is not updating in time.
To check that you could set DNS on your windows to 184.108.40.206 (google dns) which reflects dns changes properly.