MKR Motor carrier shows inconsistent Encoder speed readings with WIFI 1010

Hello,
I ordered 20 pairs of MKR Motor Carrier with MKR WIFI 1010 boards for teaching purpose.
They are connected to standard power supplies and to DC-encoder motors.

I ran the Motor_test_encoder.ino example with a 1 second delay, duty cycle setting and position reading seems ok but and I get a strange velocity reading, which should be around 100 times larger:

19:49:18.471 -> M1 Duty: -20
19:49:18.471 -> Encoder1 Pos [counts]: 0
19:49:18.471 -> Encoder1 vel [counts/sec]:0
19:49:19.474 -> M1 Duty: -20
19:49:19.474 -> Encoder1 Pos [counts]: 445
19:49:19.474 -> Encoder1 vel [counts/sec]:5
19:49:20.477 -> M1 Duty: -20
19:49:20.477 -> Encoder1 Pos [counts]: 956
19:49:20.477 -> Encoder1 vel [counts/sec]:6
19:49:21.479 -> M1 Duty: -20
19:49:21.479 -> Encoder1 Pos [counts]: 1461
19:49:21.479 -> Encoder1 vel [counts/sec]:5

I get the same issue is with a MKR FOX 1200 board which displays only 0 values. Because of the bad Encoder reading the PID functions seem also not working. I've made the firmware update to the last 0.11 version. Btw, the flash update with the FOX 1200 didn't work at all, I could do it thanks to the WIFI 1010.

Are these boards really compatible to the MKR Motor carrier?

I don't have MKR Zeros to test. Thank you a lot for any answering.