Power output down by 50w and resistance feels high on flats and small inclines

Have been riding on Zwift with Elite Direto connecting both via BLE and ANT-FEC via PC. Since 21st Sept my average power output has dropped from 200w to 150-160w. Doesn’t seem to be dropouts but resistance seems high on flats and inclines of 1-3%. Trainer calibration checked with Elite. Contacted Zwift who say this is likely to be new rolling resistance feature and suggests I ask forum whether any other bikes/tires might help! Anyone else having this problem? It is really frustrating as constantly at the back in races with no hope of catching!

@dot_gitignore is corect.

Zwift will show the power number that your trainer sends it. The roads will affect the speed but not the power.