I have two smart trainers, Tacx Vortex and Tacx Neo. Trainers are calibrated and current software is installed.
So now i have a ftp difference of 120 watt.
If more riders have the same issue, races cant be fair.
Is your vortex over reporting power and is 120W too high?
That would be bad, I have a vortex and an FTP of around 120W 
But seriously I do wonder how accurate my vortex is with no independent means of calibration. I tend to treat my watts as vortex watts rather than real SI units, with the aim to increase my relative performance.
But I agree if you are racing then having good accurate numbers is important.
I would be interested to hear from any vortex users who have managed to compare the power reported from the back wheel on the vortex to a trusted second source such as pedals or hub.
Sounds like a faulty trainer or poor calibration. My bet is that your Neo is more correct than your vortex.
They aren’t. That’s why results should include the make and model of trainer in my opinion.