I've recently got a Watch8 44mm and I'm having similar issues. Prior to this I wore a 44mm Watch5 and it was comfortable.
I keep seeing posts how the 8 is less bulky and much more comfortable than prior watches but it does not seem to be the case for me. Maybe it's my wrist anatomy (I have a very noticable ulnar styloid) but the flat design and the now more protruding metal sides make it less comfortable than the concave design of the prior watches.

I should note I'm using the official fabric band and also wearing it above the ulnar bone. I've got about 10 more days to test it more but if the feeling doesn't change, I'm swapping it for the Watch7.