Personally I use Raise to Wake exclusively being available since the iPhone 6s.
But I wonder how many of the above users have both Raise to Wake and Tap to Wake enabled?
I have an iPhone SE 2 at the moment so TtW is not available, that was introduced with the iPhone X when the Home button was removed.
So, I wonder if there could be a conflict between the two functions?
Easy to check this; Turn both TtW and RtW off, restart or turn the iPhone then turn it back on and enable TtW.
If it now works as expected you could try turning RtW back on. If this results in the same old problem then one or the other will need to be turned off as there is clearly a conflict between the two settings.
Sadly, I cant test this theory as I don't have TtW, indeed it may not be possible to turn both off. If so, simply turn off Raise to Wake and restart.