Thanks for your help, JustAMacUser
There has been a problem with my TTRSS icons since a couple days ago. Some of the icons disappeared at night, but they would come back the second day in the morning. I have tried “force debug”, and it works. But I don’t want to do it for all my feeds one by one. It seems to be a bug. Here is a screenshot when the icons are missing and refetched.
Some feeds cannot get the icon back even after a few times “force refectch”. Like the 3rd feed “solidot” on my screenshot above. The site URL of that feed is https://www.solidot.org and it does have a favicon.
In my opinion, once TTRSS finds a favicon, it shouldn’t refresh it every 12 hours unless the user force to refresh it manually.