Now I did the following:
env ASSUME_ALWAYS_YES=yes pkg-static bootstrap -f
After that I went to System Update and it showed that I have a new Version available. Before that it always showed that 2.7.0 is the latest version for PfSense.
So I updated from 2.7.0 to the new stable version 2.7.2
After it upgraded and rebooted (it felt like it took much longer than usual)
But now it seems to work somehow. The package manager shows items and the crash report does not show up anymore. I think the issue is no more. (I hope)