That is certainly not normal behaviour, all the pads should require the same force to trigger. Only a MkI user here but out of all the gear i’ve owned with pads the Rytm lands at the very bottom in terms of responsiveness and reliable velocity. Mine has gotten better with use but still wouldn’t rely on it for live finger drumming compared to my MPC.
Sounds like you may have a fault, I would open a ticket with Elektron and see if they have any quick recommendations to try before sending it back.