The resonant frequency can vary greatly between motors, even with the same drives. Larger motors are more likely to be affected.
It's unlikely that something is wrong with the steppers.
As suggested, Geckos would
probably fix the problem.
Unfortunately, a lot of people are getting sucked into these poorly matched kits on Ebay, thinking they're getting a great deal. Instead, they have to spend more money to get a good working system.
Since it's my video you linked to, I'll comment.
Without the damper, it wouldn't run any faster than 115ipm, and was stalling at that speed. Most of my cutting is done between 100-125ipm, and it's still running smoothly.
The resonance on my router occurs at almost all rpm's. If a setscrew on a damper happens to come loose, it'll stall almost immediately.