Incomplete Shed

So, the first two times he shed absolutely fine, perfect and in one piece. But this time, for whatever reason, he retained a bunch along his spine, neck, and ripped scales off his head during the process.

He's not bleeding and my GF and I gave him a towel rubdown to remove the remnants, but it's definitely bald on his head.

All husbandry is the exact same, I dare the humidity is even better this time since the AC is running less and so I've been able to drop CHE temps. Regularly seen humidity at 90, let alone 80%.

Only issue I can see is that for the last two sheds he's refused to come out of his hides to deal with it by rubbing on things in the enclosure. Not sure if there's a way to discourage that or if it's relevant.

Any ideas short of hitting that tub upgrade ASAP?

does the enclosure have anything rough for the snake to rub against?

also, are you POSITIVE your humidity is where you think it is? at 90% it's hard to think of a snake having shed issues, but some snakes just can't get that perfect shed.

you say he's had a perfect shed before, so i can almost guarantee he'll have one again. just keep a close eye on the humidity next she'd and see what happens.

He's got lots of plant garlands and is on a coarser substrate. But chose to stay in his hide (which both had moss in them to boost humidity). 90% was peak but the lowest I've seen it is 65% which is when I mist. So, kinda at a loss. Full water bowl too.

Also ate no problem immediately after his bath/scrub and isn't otherwise showing any signs of stress. Don't know why he was so insistent on not coming out to shed.