I just found out that all my events on my fairphone calender are missing. Thus I checked DAVdroid and found out that the account I use to synchronize my calender (a posteo-account) doesn’t exist any longer. I tried to set it up again, but after entering all relevant information (following those steps: ahttps://posteo.de/hilfe/kalender-und-adressbuchabgleich-mit-davdroid-android) the app doesn’t react when I press the top right arrow to continue. I restarted my phone but the problem remains just the same.
BTW my events are still saved in the posteo-account, I can access them via my computer.