I pulled down the build, and I do not observe the problem with this build.
However, Kicad can’t seem to recognize the libraries, although i can see them where Kicad is looking. So the shematics have no symbols. So, either the problem has been fixed, or the problem is somehow related to the loaded libraries.
I spoke too soon. I pulled up the nightly build on another file and I do see the pause after each action. This is without any libraries, of course.
I then reverted to 5.1.7 after a complete kicad removal, and I now see the slowdown on 5.1.7, whkch I never saw before.
I do notice tha redraws are painfully slow, painting line by line.
No problems with PCBNew. It almost seems as if using unaccelerated graphics, but as far as I can tell, eeschema is using accelerated graphics. In "“Preferences”, the “Modern Toolsset (Accelerated)” option is checked.
Interestingly, the Windows version of KiCad running under Parallels seems to work just fine (except zooming happens in big steps compared with the smooth zooming on Mac).
I haven’t been following the thread. But check the canvas for EESchema (can be set separately from the PCB canvas). The lagging almost sounds like the software rendering of the fallback canvas (F12) instead of the hardware rendering of the accelerated canvas (F11). But I could be wrong…
Fiddling with acceleration on 5.1.8 didn’t do anything. moving back to 5.1.7 retained the issue, against all expectation. I thought it might be an OS issue peculiar to my machine (and maybe it is/was), so I upgraded to MacOS 11.1 Big Sur, but that didn’t change the behavior either.
I have no idea why the 5.1.9 update fixed the problem, but I’m sure glad of it.