zwift no longer controls resistance on climbs since using erg mode on work out 

During which it would drop in and out of erg mode .

erg mode on trainer road still working so not the trainer 

I have been using for 8months and would hate to have to leave but it’s a major part of the fun.

You need to do a support ticket. When doing workouts in ERG mode the terrain changes have no impact on the trainer resistance.