Wait, you used the green tub stuff for tile? That's the premixed mastic, not a quick-set mortar. Mastic can't handle a full day's pay worth of tile weight and stays gummy forever. You need a powdered thinset that you mix with water, the kind that cures hard. That green stuff is really only for small backsplash pieces.
Totally had a similar moment last year when I grabbed the wrong bucket for a little backsplash project and spent the next three days peeling tiles off the wall while questioning all my life choices. Sandra_black is spot on about that stuff never fully curing, it just stays this weird sticky goo forever like old gum under a desk. I ended up having to chisel off a whole row because the mastic never grabbed the big subway tiles, and they slid down the wall overnight (not my finest moment). Now I always double check the label before mixing anything, because learning the hard way is just the worst teacher.