ERG mode changes since march 2018?


I’ve just started using Zwift after training outside throughout the summer.

When I “left” Zwift i march I regularly (almost daily) had a fatburn/ sweat session in then morning while following TV series/ podcasts. My ftp was 256W by then and I usually had a “60min riders choice” session with ERG mode activated. I than set my ftp in the startup window for the 60 min riders choice. Trainer difficulty set to 50%.
This resulted in an hour at approx 200W.

When I moved my bike inside this week I was trying to do the same thing - 60 min riders choice, 256W set as ftp and trainer difficulty remained the same. Now I’m only getting approx 160W for an hour.

Has anything changed in the meantime causing this to happen? Eighter with the ERG-mode, trainer difficulty or anything else connected?
Am I not supposed to use my ftp (256W) in the “60 min riders choice” startup window any more?

Thanks in advance