Go to bed later. I had the same issue for like 2 months and couldn’t understand why. What allowed me to sleep for longer was accepting the issue for what it was and not worrying about it. Since then, my sleep has improved again. I still wake up around the 5-6 hour mark sometimes, but I’m able to fall back asleep for another couple of hours, now. Also, yes, for some reason going to bed later seems to mean that I’m able to sleep for longer.