Messages on mac suddenly not displaying any image in any contact thread

This is getting weirder.

I finally received some messages with attached pictures yesterday, and they were visible on both devices, but they disappeared from macOS Messages app after the macmini activity had been suspended by "scheduled sleep" at night.

Just to be clear : everything is fine in the iOS app. All attachments are displayed on the iPhone.

Exploring the content of the attachments folder in my user’s library, i found out that some images received years ago are still stored locally.

I navigated back to the very message that contained them originally and i can confirm even those locally archived images are not displayed nor accessible by right click actions.

Another folder in user/library/cache, strangely named "com.apple.mobileSMS" is containing the previews of the recent images (even those that never appeared in the app). They are in a .ktx format. None of them is visible in the Messages app.

I have spent some time searching the web for solutions and so far no trick could repair that bug.

There is still one i did not try : disconnect Messages from iCloud, clear EVERY conversations and then reconnect and wait until macOS Messages has re-downloaded the 3.5GB of stored messages.

I’m a bit worried that things could just get worse.

If anybody already had to try that method, please let me know if that could be helpful on such kind of troubles...

Thanks a lot !

I also rebooted both devices of course...