As an update on this, I created blank new 5.1 project, imported MetaHuman there and saw that the grooms are way smoother than in my 5.1 project (upgraded from 5.0).
Reference picture (Left - Blank 5.1 Smooth Hair | Right - Upgraded from 5.0 to 5.1 Messy Hair):
Does anybody please know what I need to do in order to replicate this Hair smoothness from the project pictured on the left to the other?
Thanks!