Non 24 hour sleep cycle
My son's sleep pattern started to deteriorate during 2020, when he was about 14. After several false starts with medical professionals, he was finally diagnosed with delayed phase sleep wake disorder. He usually goes to bed at ~11pm, but is never asleep before 3am*. We have to wake him at 12.30 to try and keep some routine in his life otherwise his sleep could end up all over the place.
One of the treatments suggested by a sleep doctor actually made his sleep patterns worse.
There is a risk that he could fall into a 'Non-24 hour' sleep cycle, there is also a slim chance he will grow out of it.
He's also been diagnosed with ADHD, but it's not clear if the two are related.
* Yes, we've done all the screens off, no blue light etc. His bedroom is as dark as we can make it. He just lies there in bed and can't sleep.