I can see the software cutting your speed down to zero, so it is engaging something, it just isn't seeing the shift key down.
I retested on my computer using an Apache and I did get one instance in about 30 where it didn't process the shift key, it was right after I had used the Alt key for Altitude-Hold. I held shift down and tapped "H" twice (Hover Off then back On) and it reset and worked properly.
OK, I was able to duplicate your problem in a Ka-52 Alligator. It wouldn't control the collective no matter what I did. The Ka-50 Blackshark worked. The Ka-52 worked the second time at a low altitude, but it wasn't locking onto the correct altitude when I turn it off and on again. It looks like the altitude variable it uses (from the Razorworks code) isn't consistently updated, I'll have to use a different variable in the code.