I am using Xert indoors on a Tacx Genius Smart trainer and a Power2Max powermeter. I use the power match feature where the power meter controls power, as the power meter is of course the best source of power data. However, what I am seeing is that i need to put out a power output around 20% more than the power prescribed by the Xert workout. Any ideas as to what is going on here? I have used the similar power matching feature in Trainerroad where it tracked perfectly. Obviously a power output 20% (or more) above what is stated in the workout is not ideal, although I guess it will make me fitter… 
Send a note to support@xertonline.com with details on which app you are using and what configuration you have.