This is the teenage thing that absolutely scuppers some folks and it is one of the reasons so many dogs land in rescue - the 'good period' followed by the 'horrific regression' that leads people not in the know, to believe that they've fucked up or the dog is an incurable twatbag.
Bit like humans, as they learn and process and habituate, the brain gets... full. A lot of learning happens when we sleep/relax and the teenage mind struggles with that, so theres things that aren't being committed to long term memory that should, things that are just being cycled round and round, and also like us, the more they learn the more they have to do, the harder things can then get... and boom, we hit the 'can't cope/won't cope' fuckwittery meltdowny behaviours.
The clothes bitey/humpy is his version of slamming doors, having thoroughly unsuitable friends and saying FUCK in front of Grandma to see what happens.
Do whatever you can to take a break, shorter walks again, quieter times, dead of night/pissing rain storm etc etc - lots more chewy/scattery stuff.
Going back to management you used a month or so back is NOT a failure, meeting his needs where they're at 'right now' is sensible, not in any way 'giving up' or losing progress you've made.
He'll get back to that, and he'll get there faster than he did last time. And he will probably regress again... and it will probably be an even smaller blip... and eventually it will be such a long time you'll really only remember what a total bell-end he was by reading these threads back.