In the meantime, FSDreamTeam has taken many complaints and errors seriously and made some updates. I have then only once the previous installation completely deleted from the computer, including registry entry, then downloaded the latest installer.
After this installation everything runs better, but with many errors, for example, editing the pushback does not go properly as it should be. Now my GSX Level 2 for P3Dv5 is completely gone, but in MSFS it works reasonably. So you can install it if you accept the still existing bugs. We don't get the money back after all.
Who has a bad unusable version ( as I had it) should however once wipe everything clean and then run the latest installer and updates.