I've rebooted the system but it didn't solve the problem. Diagnostic zip file has attached.
I also re-checked both the Update and Downgrade page and they only loaded contents from the local server and nothing from other domain(s).
alexhomeserver-diagnostics-20240218-1936.zip
Recently I updated my unraid server from 6.12.6 to 6.12.8, and after the update, the version number doesn't show up on the top left under the unraid logo as usual. And when I access the Update / Downgrade OS in the "Tools" page, both pages show nothing but an empty page. I tried to restart nginx but it doesn't solve the problem.