Request of desktop client times out

Hi everybody!

For some folders the desktop client times out with the following message in the error log:

[Fri Jul 23 17:46:57.911741 2021] [proxy_fcgi:error] [pid 98:tid 2719994912] (70007)The timeout specified has expired: [client] AH01075: Error dispatching request to : (polling)

The folder contains round about 16,000 pictures (200 GB).

If I open it via the web client it does take some time but the files are listed.

Any ideas how I can find out exactly what happens until it times out?