SUMMARY
The plasma style "Breeze (follow colour scheme)" won't be retained after a reboot of the system, it will automatically set the global theme as plasma style.
i.e. If i set global theme=Breeze Dark it will always set plasma style=Breeze Dark when I choose a style with "follow colour scheme" feature. If i select any other plasma style it will be retained instead.

STEPS TO REPRODUCE
1. Set the following in System Settings under Appearance:
   global theme:Breeze Dark
   plasma style:Breeze (follow colour scheme) 
2. Reboot the machine

OBSERVED RESULT
Plasma Style is set to Breeze Dark

EXPECTED RESULT
Plasma Style is set to Breeze (follow colour scheme)

This is important because if you choose a different colour scheme (i.e. Breath) the plasma style won't follow that colour scheme, causing an inconsistency between the plasma shell (i.e. panel, tray applets) and the global colour scheme

SOFTWARE/OS VERSIONS
Linux/KDE Plasma
KDE Plasma Version: Plasma 5.20.5
KDE Frameworks Version: : KDE 5.77.0
Qt Version: 5.15.2