Messages attachments not displaying after update

Yes, it works in the new user account.

I also observed in my main (not working) user account, attachments appear correctly when they are received, but after rebooting they are no longer displayed.

In the test account, attachments continued to work after a reboot.

I also tried copying my not-working ~/Library/Messages folder to the test account. Attachments then were missing, so it's not some account-level difference: probably something about the Messages folder data.

Hmm, the update had "improved input validation" in Core Data. I wonder if my messages database is slightly corrupt? But

sqlite3 chat.db "PRAGMA integrity_check"

returns "ok".

In safe mode, the conversation part of the Messages window was pure black. (There were also some other visual glitches while starting, such as the login window getting cleared and redrawn almost line-by-line, as if the graphics driver was very slow; I assume there is only a basic graphics ability in Safe Mode).

Restarting again not in safe mode, the attachments are still not displayed. I got a new photo sent to me, and now the conversation shows "Attachment: 1 File" but the attachment (a live photo) still isn't displayed in Messages.

Eventually I can try messages in iCloud and see if that helps, but I don't want to risk it syncing the corrupt version from my Mac instead of good versions on my iPad and iPhone.

What should I look for there? Among many others, it has a Messages directory that has symlinks to my ~/Library/Messages directories (some by relative path, ../../../../../Messages/Attachments, some by full path, /Users/<myname>/Library/Messages/StickerCache).

Here's a log from Console.app, reported from Messages (IMFoundation):

[Warning] Couldn't associate fileTransfer with guid: 7C3B55E7-F7A6-4845-9E77-4C020041053B for message: IMMessageItem[outgoing: YES sender=(null); service=iMessage; handle=...

That guid is the name of a folder under my ~/Library/Messages/Attachments and I can open the jpeg in it in Finder.

And there are many more similar messages. This probably just verifies that Messages tried to open the attachment but failed. Logs before this don't show anything promising; this message is repeated several times in a row (with different guids) without any other process logging anything in between.

Thanks for the continued suggestions! I repaired permissions according to https://support.apple.com/en-us/HT203538 on ~/Library/Messages and ~/Library/Containers/com.apple.iChat and no change.

I hesitate to repair permissions on my whole home folder because of https://eclecticlight.co/2018/07/14/should-you-try-repairing-permissions-in-high-sierra-or-later/ and because I'm not suffering any of the symptoms Apple says it fixes.

That just has Container.plist and the Data directory.

Temps are between 38 and 46.

I poked around in ~/Library/Messages/chat.db with sqlite3 and it has an "attachment" table with valid paths to the attachments. I also tried replacing it (temporarily) with a backup from a couple days ago. That made Messages show only the older messages, but still no attachments. So probably not a database corruption issue?

I see that Messages.app folder shows a last-modified time from this morning, when I installed the update, so maybe the app was part of the security update and some change in it is causing my trouble. I might try finding a slightly older version of the app to test with.