Probably seems silly, and self-induced, but I noticed while riding Norway that in the last 15 or 8 seconds of an up segment (not sure if there is agreed-upon language for describing the patterns of wattage expectations here), my cadence would drop to a speed that I surely wasn’t doing.
Toward the end, for the last few, I’d fight the hell out of it by maintaining 107 RPM or better throughout those last 15 seconds, and yet I’d see it again and again. Not every time, but enough that - especially when not seeing it elsewhere during the up-segment time (40 seconds per IIRC) - it suggested that it wasn’t my cadence sensor losing connection / data with the dongle I have. I’d see it flash something in the high 80’s on the screen during these ‘down cadence’ readings, where-as at the very end of each up-segment I’d be back up well over 100 RPM (because I never left over 100 RPM).
By the way, this is the 'dongle I’m using. Feel free to lead me to a better system. I honestly don’t know what else is out there, and bought it just to get my trainer up and running. I’m using a Wahoo cadence sensor on the crank arm.
CooSpo USB ANT+ Dongle with 6ft. Extension Cable Compatible with Zwift TrainerRoad Wahoo Garmin Cycleops Trainer Rouvy TacX Sufferfest PerfPRO
There’s sometimes a ‘stickiness’ to the wattage, too, where it will keep the 2021 Wahoo Kickr at high wattage even though it’s supposed to be at a low wattage. If the down-segment has enough time it eventually will start dropping, but if it’s a quick down-segment between up-segments, it often won’t let my trainer release to the lower wattage expectation.
That may be a training issue where I’m doing something incorrectly for SF or for the trainer, but I don’t know.