The culprit is NOT the magic keyboard it is BlueTooth and the design of the code. There is nothing you can do right now. Whether it will be fixed in MacOS 10.15 (Catalina) or not I cannot tell. To be honest I don't really notice the problem one way or the other, but IIRC it has come and gone in various releases of the betas. At the moment it is gone, but until the Golden Master is released we won't know exactly what changes will be in it.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein