I get lower rpm readings on large cassette chainrings.
My current setup is 50/34 with 11-36 mounted on a Wahoo Kickr Core and using a wireless crank mounted Wahoo cadence sensor. Everything works fine on all gears except the 34-36 combination where I get the rpms show half the value of all the other speeds. I had a 11-32 cassette before and everything was fine. The second gear going down on the 11-36 is a 32 and it works fine.
Considering that you don’t have to enter the details of the bike setup on Zwift or Wahoo material I don’t understand what’s going on.