Feels like trainer difficulty is different from race to race

Hi guys. Due to the covid fun I get to race alot these days. But one thing I dont understand: For me it seems like the trainer difficulty kind of varies from race to race at the same setting

I am happy with it set at around 50% (or maybe 60/40 over to the hard side). Makes me not changing gear so much but still have some resistence to get out of the sadle in the hills. But at some races, as of to day at the Instruck ring, it is way to little resistence. I am not able to stand out of the sadle at the hills and the cadence is sky rocketing at the sprint. Is this just me?

Is this a variable thing calculated from HQ from the gradient of the course or something or just a bug with the system/trainer that occure at some unlucky times. I guess for me it has happened 2 out of 10 races.

Cheers (hope you understand the question)