I am having a similar problem. The Twinsync appears to be setup correctly. I get a green led lighting correctly for each sensor, both yellows com on at the correct low end sync point, and I am ignoring the reds as I am running 2 x Evolution 26cc gassers. The problem I have was initially only at full throttle after about 10 seconds both engines would suddenly drop back to half throttle. Moving the stick back a fraction would bring both engines back up to full for a matter of seconds then they would drop back again. The problem got worse and worse over the next half tank (on the ground now) until I was unable to advance the throttles at all without them chopping back to idle. I played with the sensor mounting and got some improvement, but still not good enough to fly. The sensors are mounted on aluminium brackets that do have a fraction of give in them. Running cable ties around them to take out any play made the problem worse still. I have also played with distance from the magnets to the sensors - nothing conclusive.
I am wondering if the problem is caused by the two magnets on the Evo motor. They are opposite polarity and the green led is only turning on once per revolution so only picking up one magnet, however would there be field interference caused at high rpm by the other magnet? Clutching at straws here. The system is in an ESM F7F so I would rather not have to mount another set of magnets if I dont have to (means using a spinner backplate and would look weird).

Thanks in advance for all your help.