I have a Direto, too. I can’t say I’ve paid close enough attention to know if I have the same ‘problem’ (only one FTP test on the Direto so far, and one 60 min rider’s choice).
Per Zwift support “A: The actual FTP test portion holds a flat resistance, so you’ll need to change your gears to increase/decrease wattage, like you would on a regular ride.”
Now, it’s well known that when ERG mode *is* active, Zwift is not particularly strict re: holding *exactly* to a given power target and if one isn’t really consistent w/ cadence that the Direto wanders around a bit trying to dial in the correct amount of resistance.
What’s not clear is what is meant by ‘holds a flat resistance’ and whether or not the Direto wanders up/down trying to hold that in the same way that it does w/ power targets in ERG during workouts.
My gut feeling is that it doesn’t. I’m familiar enough w/ the ERG mode variability and I can’t remember feeling anything like that during my FTP test. I thought I read somewhere that Zwift holds a fixed 1% grade simulation during the test portion. My Direto has (so far) been very consistent when it comes to applying resistance on hills in SIM mode (aka ‘Just Ride’) - so if that’s the case for FTP, then there shouldn’t be any noticeable changes in resistance. Only the pain and eventual cracking of legs and morale!! ;)