Bonjour danicolas07;
Just to make sure I understand; it worked at first and then stopped working? Did anything change between the time when Autoptimize worked and when it stopped working (a new plugin, a plugin update, ...)?
Most references to those types of errors are with PHP running out of memory, so maybe you could test with a higher amount of memory allocated in your php.ini?
Additionally, can you try disabling HTML, CSS or JS optimization one after the other to see if one of these is to blame?
Bien à toi,
Frank