you can try to install and activate WP Safe Mode to narrow down the problem and see if this is due to a conflicting plugin or theme.
https://ww.wp.xz.cn/plugins/wp-safe-mode/
Hey, I got the same problem.
I can not change settings for the event manager. If I press the save button its starting to download the edit.php file too.
All other settings I am able to change.
I read about, that it might be related to the max_input_vars.
Value appears to be 4000 right now. Currently trying to change for 10000 (nothing changed in the last 24 hours)
As I am still a beginner in wordpress, I would be thankful for any support.
List of plugins:
Display Posts
Duplicate Post
Elementor
Events Manager
Ocean Extra
TablePress
Aktivieren | Löschen
WPForms Lite
Yoast SEO
Themes: OceanWP
Problem solved.
It was most likely the max_input_vars value. Probably its not enough to wait 24h after changing.
After 72h it was possible to save my seetings for the event manager plugin.
Thanks for the update and for sharing the solution.