A few weeks ago we finally upgraded from the old version (8451 from Feb 2023) to the new version.  Ever since then, we've received some complaints-- and have noticed ourselves-- that browsing to a page in the web interface results in a partial page load (usually the underlying page template) but the main content (mailbox contents, admin options, etc) never load.  It's just a perpetual spinning donut.  But refresh the page, and everything immediately loads fully.

Server load doesn't seem to matter.  Even late at night when the system is nearly idle, minimal traffic, it's the same behavior, so it is clearly not a system-load issue.  In the daytime, on the new version the system almost never goes above 10% CPU or 60% RAM, and the disk subsystem has a ton of available headroom, so there's never a time when it's under anything more than light to moderate load.

It was exceedingly rare for this to happen under the old versions.  Wondering if anyone else is noticing this.