After finding the scissors tool causing sluggish jerky redraws, after a few minutes,
it took me a bit longer, to find the reason for the 2nd issue
(Jerky redraw, depending on what is shown in the project window) :
It is caused by very long MIDI parts.
As the integrated click is very limited and many of it’s options do not work,
I have to resort to using MIDI click tracks.
As I mostly record different takes in series, I need very long click parts.
That’s why I had the jerky redraw, when the click tracks where in view.
To repro :
Create a MIDI track.
Create a 4 bar MIDI part and fill it with notes.
Repeat that part 300 times.
Glue all copied parts to one.
Zoom in to see 8 bars and start playback ( stationary cursor = on )
Split long MIDI parts into short pieces.