You may be running into a power floor. A power floor (also known as a “wattage floor”) in ERG mode on an indoor trainer refers to
the minimum amount of resistance or power a smart trainer can apply at a given flywheel speed. When the target power for a workout interval (such as a low-wattage recovery period) is lower than this physical limit, the trainer cannot drop its resistance any further, causing the actual power output to remain higher than the target