Calendar lockscreen notification not working after 1-2 days

[joadoor]

Hi there in the forum,

I've the problem that my lockscreen calendar notification (S-Planner or Digical) ist not working after 1 or 2 days.
The rest of notifications are working (gtask, phone, whatsapp, threema...)
I've set the notification on and the energy-saving to off...

no idea why this stops working after a while...

For some ideas I'll be VERY happy

Thanks
-joadoor-