Index search under load

Hello everyone,
we have a treadmile that we want to run with a t-motor u13 kv85 and AMT102V attached to it. I calibrated and tuned the motor with no load attached and it worked. Now I attached the belt of the treadmile to the motor so that the motor can run the treadmile. Unfortunately the index search is not working anymore. As soon as I start index search the motor oscillated forward and backwards without finding an index. The motor itselfs has a high cogging torque so I had to set the calibration current to 20 A previously. With the load attached the friction increased but rising the calibration current to 40 A didn’t help a lot so far. Any ideas? Is it possible to do index search with load?

Thank you very much for your help!!