So, I tried resseting the AP (actually bought gold for that) and...

I upgraded accordingly, then needed an F5 because my screen froze.
Credits are taken (-150) but AP was restored to initial values.
Then credits are back, but AP stilli on initial values.
Then, some territory's I took, went back to neutrals...
Then credits are gone again.

Now credits are taken (-150), AP still at initial value (before I reset it), and my game went back on neutrals I already conquered...

I wanted to take the Auto Conquer for the challenges/battles, and it seem it won't let me. (Oh, but the credits withdrawel works flawlessly, of course)

I'd suggest to file a (bug) report directly ( https://www.warzone.com/Contact ). I assume Fizzer won't read the forum 24/7.

Then, some territory's I took, went back to neutrals...
and my game went back on neutrals I already conquered...

I can at least tell you what I suspect happened here. The game only syncs every 10 minutes or so (the wiki has an exact number somewhere). If the browser (I assume this happened on PC) invalidated its cache while reloading the game, you would see an older version of the game. This can also cause problems if you switch between PC and the apps. The apps have a Sync-Button in the User-Menu (the head in the top right), on PC you can force a sync with "Ctrl"+"Alt"+"G" (though, you don't get a feedback when the sync was successful, I keep the sync on for a few seconds to make sure).

Did you have multiple instances of the game open simultaneously?

I was using the simultaneous play, so yes.

Meanwhile, I finished one of the two games, hoping for it to trigger my reset, but nop.
AP's are gone, but reset didn't take effect.

Z might have meant whether you were playing idle on multiple devices simultaneously.

I was having two instances open, since I used multiple play.
One on chrome, one on firefox.

The problem was solved anyhow, so I'll watch out for that synching next time.

If I remember correctly, Fizzer answered somewhere that even with Multi-Level active it might/will/could screw your game states if you run your game in several applications at the same time. But I could be wrong.