During the last summer, I messed up a large amount of pictures with my Z6. After many checks, I found out the culprit : (it was me actually) :
The ''Disp'' command was on Video mode instead camera mode...
I had tried the video mode long time ago and I am sure I had switched the command back to ''camera''. So, I might have done it inadvertently ?
The result was a lack of resolution on all this pictures until I found the issue !
Once I changed the ''Disp'' button on ''camera'', everything went back to normal...
BTW, I didn't see any warning notice displayed on any screen.