Cadence does not work on Zwift

The cadence will be stuck at 1 rpm, suddenly jump to 215 rpm, then back down to 1. It never actually shows my real cadence, this is super annoying! It was working fine and I was racing on Zwift and suddenly in the middle of the race it just dropped to 1 and I haven't been able to get it to work since. Any suggestions? Please help.