I'd suggest you create a super simple project with 1 sprite and see if that works.
If it does, do you have large files? Are you on your home/office network? (I don't have a lot of luck remote testing on networks in places like coffee shops)
Then I remove plugins one by one until it works.
Can you share which plugins eventually was the culprit for you?
I'm having the same issue for awhile now. I remembered being able to remote preview 1-2 months back but out of nowhere the feature suddenly stopped working for me.
I also tried opening the older script from before when I was still able to remote preview but still not working. Tried using the latest Beta version or different browsers doesn't seem to do the trick as well.