strange printing error...any leads?

[tease]

Hello Eveyones,
(free foks or quarantined!)

I'm fairly new in 3d printing, but had very good result so far.
Until I tried my bigger piece,  that came out with a strange error: 

it print half way fine, then made a a first sort of square plate, then printed 1 more centimeters, then swalow all the resin in a big solid block...

here are 2 pictures:


did the Z axe had a little stop, then a big one?
I don't think I had a change of temperature during the night of printing, but its possible.

Do somebody have an idea of the cause?

thank you for your help,
best quarantine or enjoy the free world while it last!