When using ERG mode I used to make the error of chasing target power without looking at my cadence.
Slow your cadence and keep your pedalling smooth and consistent and let the ERG mode calibrate the power. After a few seconds you’ll find the trainer self corrects to the correct wattage as long as you’re consistent.
I’m now trying to keep the same cadence throughout a workout including recovery. It doesn’t always work but it certainly helps smooth out the power output whilst utilising the pedalling drills to keep everything as smooth as possible