On both of the different FFB sticks I have had in the past, I'd experience something similar when the "deadman's switch" would engage - which would happen at times when I simply shifted my hand position. On both the Logitech Wingman Force (not the POS 3D, but the original stick with the 20 lb motors) and the MSFF I ended up defeating the sensor because the stick would go dead and I'd slam it to the stops when the resistence suddenly disappeared.
(Made for some interesting flying when that would happen)
You might try something similar and see if it eliminates the issue. I found that on one, I needed to tape a reflective material over the sensor emitter pair, and on the other, I used black electrical tape to "permanently" interrupt the beam.
I'm mentioning this because while I don't have a G940, in both instances with the sticks I had, it wasn't immediately apparent the problem with loss of FF was simply because the stick "thought" I'd let go.
<S>