It might help to see the workout in question here, specifically including power and cadence. A link to your workout if you TR account is Public is great, but a zoomed in screenshot can be workable too.
For reference, here is my latest workout of this type, 30/15 VO2.
This is with my Kickr V3, but I had similar results back when I was using my Saris H2. Essentially the same trainer as yours other than the drive belt and pulley.
As ever, cadence is key in ERG workouts, and possibly more important in these types of efforts. It can be tougher to handle the changes, but you need to get to and hold your desired cadence as steady as possible.
Also, gearing can impact results. Trainers perform best in moderate gearing as opposed to higher gearing. Using the small ring and middle of the cassette is best WRT trainer action. I use the 34t x 17t and the trainers all respond quickly and predictably.
Generally speaking for this type of effort:
- I roll in about 5-15rpm lower cadence than I aim to use for the work intervals.
- I kick up cadence right as the interval timer hits the start. This is 1-2 seconds after the trainer actually gets to upping the resistance level, since TR sends that instruction about 2 seconds early on purpose (to handle trainer adjustment lag).
- Once in the early seconds of the interval, I try to stabilize at my desired cadence and then hold as steady as possible until the end.
- At the end, I slowly reduce cadence against the faster spinning flywheel and lighter resistance, and then ready myself to repeat it all.
As you can see above, even with as short as a 15s recovery, I am hitting the power targets (more so the trainer) with some peaks in the process as I am kicking up the cadence. Other than that, it is predictable and holds targets as desired.
For those that want to, swapping to Resistance or Standard mode is an option and one that might make more sense. But it is possible to rip these workouts in ERG if that is the preference.