JEM keeps showing just the same 3 events

hi, 
I've been struggling for days: Only the same three events are displayed (out of 1200) everytime.

I've already deactivated the template, set Cassiopeia, and deactivated all plugins. I also did a completely fresh Joomla & JEM installation and imported the four exported .csv files (only the last 180 events, though), then set all "created_by" and "modified_by" to the appropriate new admin ID before loading them, using the `view=eventslist`. 
Permissions are set to "use global". All status is published, all are checked in. Access is public. No trash permissions.

Any ideas? Maybe some kind of data error? What could be causing this, and how could I figure it out?
Perhaps the process keeps aborting after encountering an invalid record?

best, m.

on
 Joomla 5.4.3, JEM 4.4.0, PHP-Version 8.3.29, 10.11.14-MariaDB.

I need access to debug it. Please send me a private message.