SUMMARY
Some of the apps disappear from the Favorites screen every time the plasma starts up.
I have two Activities running. Even though I have added these some apps to Favorites for all Activities, they are missing at the favorites screen. I can add these apps to the Favorites screen again by toggling the checkboxes for Activities in the Show in Favorites context menu. But they will be hidden again after restarting Plasma or another Plasma trigger.

STEPS TO REPRODUCE
1. Add many apps to Favorites
2. Add new Activity
3. Restart plasma / Install some apps

OBSERVED RESULT
Some apps disappear from the Favorites screen despite being added to Favorites.

EXPECTED RESULT
All applications that have been added to Favorites remain on the Favorites screen and always keep the manually set sorting order.

SOFTWARE/OS VERSIONS
Operating System: KDE neon User Edition
KDE Plasma Version: 6.4.1
KDE Frameworks Version: 6.15.0
Qt Version: 6.9.0
Kernel Version: 6.15.3-x64v3-xanmod1 (64-bit)
Graphics Platform: Wayland
Processors: 16 × Intel® Core™ Ultra 7 255H
Memory: 32 GB of RAM (30.8 ГиБ usable)
Graphics Processor: Intel® Graphics

ADDITIONAL INFORMATION
The problem existed before the addition of second Activity and before Plasma was updated to version 6.4, applications also disappeared from the Favorites screen, but were restored there after restarting Plasma. But the manually set sorting order was rearranged.