This might look like a failure but it is not, found 1 station very close with exactly the same drop in humidity while we had a short wind direction swap.
Had to be a very local phenomena since other nearby station did not show it (ok, not so many where I live)
Not sure what this could have created, like a super dry bubble.
Looks like a Foehn wind blowing over the Pyrenees. The wind switched to the north, and as the air mass descended on the leeward (north) side of the mountains, it drove a large fall in humidity and a rise in temperature