Was this recoverable at any stage prior to the second pitch up?
It was recoverable right up until they ran out of altitude.
Cancel TOGA power, trim down, normal stall recovery.
The Airbus instructions specify making the test at not less than 10000 ft AGL because recovery could involve losing a lot of height. They tried to do it at low level. Simple.
Lessons to be learned :-
1) Do not allow ground staff to pressure wash sensors.
2) Assess possible improvement to sensor seals.
3) Do not conduct test flights without proper training and briefing.