Bottom line: tank slappers can be caused by a variety of issues: mechanical, road surface, rider input/action,; can originate from the front or rear; and there is no single solution for recovery.
Sometimes accelerating, sometimes decelerating, sometimes the bars will be ripped from your hands so quick and so violently that your only reaction can be to find a soft place to land, cuz there ain't no recovery.
In my tank slapper caused by bottoming the front end in a hole at speed, the bars went left first, and my pinky broke the clutch lever off at the pivot, which in turn broke my finger, then slapped right and the next thing I knew was i was on the pavement running for the edge.
I didn't know my finger was broken till I ran back to drag the bike off the road and looked down at my hand and in the glove the pinkie was sticking uup at a ver stranges angle.
Just imagine, lay your pinky on the desk, then hit it with a clutch lever hard enough to break the finger and the lever. Nasty break, took 2 pins, very painful.
I had a helmet, which was trashed, and full riding suit, also trashed. But other than the finger i was OK.