The same thing happens when you manually rotate an actor in your scene as well. So it’s not due to an error in your code or anything, it’s about decimal precision. You can try fixing this by adding an additional logic to your existing rotation code, like rounding it’s world rotation if it’s not already.
You could also try using double precision floats but if that also doesn’t work out, here’s a post I found that might be helpful 
How can I increase float precision in unreal engine 5? - #4 by EliasWick