You put me on the right track! Thank you!
Yes, I have been using a new template and various plugins, modules and components since the migration. Unfortunately, this is absolutely necessary. But these are not the problem.
I was able to identify the “Easy Content Restriction” plugin by Viktor Vogel as the cause. As soon as the plugin is deactivated, JEvets will display the entries correctly again. Unfortunately, changing the activation order doesn't help either. Only if I permanently deactivate “Easy Content Restriction” will the calendar entries all be displayed correctly.
I will contact Viktor.
Feel free to take a look on my website to watch the problem is temporarely solved
Kind regards
P.S. can you help me to make an override? The main color in JEvents view by period is red but I want it shown in my color
https://melomania.me/live/termine