I spoke to the Mr. Foster at FosTech directly.
He said the the issue was almost certainly the trigger pull weight, that the stock trigger on that particular line was generally 5#+ range, which cause the user to have to pull harder in the forward motion to fire. I agree the thing does have a very heavy trigger. This is a sort of known issue per se it appears.
The additional forward force counters too much recoil causing it to move forward again faster than the action can cycle, effectively the reciprocation is TOO efficient and I need more of the recoil delivered instead of countered, so....
It sounded like he was reasonably sure, and I would consider him to be the most likely authoritative source on his own product (At least the one that has logically used it the most and troubleshot it the most)
It is currently at local gunsmith having a polish / spring job to lighten it up to around 3#.
Either way I get a lighter trigger out of the deal, which was not an unreasonable modification to have made anyway bumpstock or no, we will see if it fixes the problem and I will let others know / post video of it working ASAP.