Hey guys,
Well it just happened to me 5 minutes ago. Found your thread about it...
Tried the "cursor size" method, it didn't take.
Then tried to think about which process could/would bring up the loading icon...couldn't think of one.
So decided to write about it there....but actually...in the process of signing into my apple ID, as my cursor was off to the side somewhere, i signed in and the next time i moved my mouse, I saw it back to the good old "arrow"
Problem solved.
Don't know why or how, but it seems signing into apple fixed it... weird.
Sorry if that doesn't help. But just wanted to say that the "Cursor Size Adjustment Method" did not work for me, and after signing in and writing about it, i was going to restart my computer, because it seemed like the only 'probably fix'.
Apple should really fix that, its weird and totally not cool. I understand it was a hick-up on behalf of the programming, and some bugs always follow a new release. Just hope it doesn't get worse...
Good luck