Thanks! I tried that and it seems that the freezing after Ctrl-C and Ctrl-X is gone - but it still freezes on a lot of occasions and it feels a lot slower than PL/SQL Developer 11 was...
Are there any solutions yet?
I'm using PL/SQL Developer Version 12.0.7.1837 (64 bit) running on Windows 10 Enterprise.
Every time I copy something the PL/SQL developer freezes for some (up to 30) seconds.
Also on other occasions like startup, connect, compile, runs sql, etc.