Are you running into the problem of resistance kicking up until you have no strength to push the pedals (i.e. the ERG death spiral), or that no matter how hard you push it's hitting a power cap?
From your description it sounds more like the latter than the former... so assuming that:
1) make sure you are not using a gear combination that is too light (e.g. 34t front 28t back for high resistance work). Some trainers, even though able to handle large amounts of maximum power (I checked your Saris spec, it does up to 2000W), but if the gear is too light it may be unable to supply the necessary resistance to handle the effort.
2) if the surge efforts are too short, you may be experiencing lag. Basically there is a delay from when the app tells the trainer to increase resistance, to the point where the trainer actually starts increasing resistance, and this lag can sometimes be as long as 3-5s especially if there is a lot of wireless interference in your area. So by the time the trainer registers the change, it may already be time to end that effort and adjust to the next one. Some apps, such as The Sufferfest, recommend turning off ERG mode for these sort of workouts and manually adjust your efforts by changing gears instead.