NameCheap went to PHP 7.4.2 seems like an hour ago or so. It might be causing this:

PHP NOTICE [8] Trying to access array offset on value of type null in sources/sitemap_ajax.php on line 571 (version: 10.0.30, PHP version: 7.4.2, URL: /data/sitemap.php?set_perms=1&keep_session=f801ad011d47f)

 

Ok, I'll get a hot-fix for that.
This is when you're saving permissions in the Permission Tree Editor I believe.

PHP 7.4 introduced some extra strictness in PHP (a good thing in itself) but there's no way to find all the issues with automatic code scanning, so little things buried in corners of Composr keep coming up.

Can you give me a hint what you were saving permissions on? I want to test the fix properly, but this is an edge case - saving on something Composr cannot see on the Sitemap.

This error seems to have been resolved. Not in the logs recently. I think this one's done for now.