When a long script is called to run, other moving sprites pause for a visually noticeable period of time.
I think this is caused by the IDE adding the glow around a running script.
Demo example - press spacebar - to see effect.
Spacebar script is deliberately VERY long to show the issue easily - you can try numbers 1 - 9 to see shorter, mopre realistic examples
My workaround is to put the script inside a dummy custom block and call it that way instead - press 0 to try that out
This is from my missile command program and it first came to light when I was using when key pressed blocks to launch my missiles and I noticed that the incoming missiles visibly paused
I thought it was to do with detecting keyboard events - so instead of using on key hat blocks - i used a forever loop
and that stopped the glitches (But it turns out that it was the putting my script inside the custom block that removed the glitches and not the keyboard hat block)
Recently, I added the bomber going across the screen after a few seconds, and the glitch came back
Then I noticed that if I put my script inside a custom block - the glitches went away
Of course, it might just be on my machine
If not and its replicable, can the "glow" effect be made more co-operative to other running processes or as a last resort - can it be made a project setting?