I’ve been using Hammer trainer for quite some time mostly trouble-free except for one thing. Cadence reading has always been unstable jumping at least +/- 10%, no matter how hard I tried to keep it smooth. Then I decided to use a Stages power meter as a cadence sensor, and the difference was immense: +/-2% at 100rpm with no changes to my pedaling technique.
Naturally, using an external cadence sensor when a trainer has its own is absurd. Maybe this is something worth looking into?