Yep, regression is definitely a thing. Both my lakelands went through a phase around 5 months where they appeared to forget everything they'd learned (apart from the naughty things lol) and it took around 3-4 weeks each time to get them re-educated. They both went through a real wilful phase in the run-up to their first birthday,
as well.
My first dog was always allowed in the bedroom. When I got the first puppy, he was crate trained and settled quite happily into his bedtime routine. When the first dog died, the "puppy" was allowed to choose where he slept which, unsurprisingly, was on my bed.
When we got the second puppy, she was a bit more of a challenge but after a couple of weeks, she settled. When she was about 4 months old, she got an upset stomach, so I moved her crate into my bedroom so that I'd hear if she was ill. She kept on and on rattling at the door of her crate so eventually l got her out and let her on the bed, with every intention of popping her back in her crate as soon as she was properly asleep.
I fell asleep before she did, and woke up in the morning with both dogs snuggled up on the bed, and she slept on the bed from then on.
Now she's an old lady, she sometimes prefers to sleep on the floor at the side of the bed. She's not so keen on jumping off the bed any more, and has to be lifted on.
Anyway, another thing that might help him settle is a short stroll, just round the block or something, last thing at night. I have a few friends and neighbours who swear by this, and there is something very pleasant and relaxing about a stroll through silent streets with a dog. (Well, maybe not if you live in some dodgy inner city...)