It wasn't a spate in the USA - there were 2, I believe. One was a departure, the other possibly related to engine failure, both out of Colorado Springs. Hondo experienced no such problems. Subsequent testing (admittedly after a fuel supply modification) failed to find any fault in spin recovery or engine response following prolonged throttle-closed gliding. Both accident aircraft were the 6-cylinder version with the low canopy.
The RAF spin accident was the 4-cylinder 160 with low canopy. All in current UK military use are 6-cylinder with the high canopy and long-chord rudder.
As with most aircraft accidents, there is no single obvious cause.
There has been generic research into escape from spinning aircraft, including that in the vertical wind tunnel at Farnborough, and there is much evidence of experience of survivors.