unified bed leveling resulting in Z-height issue

Before I used Unified Bed Leveling (UBL), I was using bilinear leveling with BLTouch. everything was fine and calibrated. a 20mm calibration cube would come out ~20mm.
But now that i implemented UBL, all my models have errors in Z height. a 7mm print became 8.5mm. a 20mm cube became 22mm, etc etc.
Is this an issue with fade height?

I am at a total loss here.