Issue with ZM 1.36.x - Event thumbnails not generating properly

[Alread]

I'm running ZoneMinder 1.36.33 on Ubuntu 22.04, installed via the official PPA. Everything seems to be working mostly fine, but I've run into an issue where event thumbnails are not being generated consistently.

Here’s what I’m observing:

When events are recorded, sometimes the thumbnails appear correctly, but often they just show as broken image icons (even though the event video plays fine).

I've confirmed that zmthumb.pl is running via cron, and permissions on the events directory seem correct (www-data owns them).

Logs don’t show any obvious errors related to thumbnail generation.

Tried clearing the cache and restarting Apache/ZM - no effect.

Has anyone else run into this issue with 1.36.x? Is there a config tweak or database update I might be missing?

[iconnor]

What is zmthumb ?

No third party add ons should be required for thumbnails... they are generated at recording time.

.33 is not up to date. We are at .35 and working on .36.