Problems with the timings of sleep, (which is what circadian rhythm disorders are) don’t always mean broken sleep.

They might sleep a full night but they just do it at a different time of day. If you don’t get to sleep until 3am every night but can’t get up earlier than 9/10/11am, you are getting the sleep you need but it’s happening at an odd time of the day.

That could be Delayed Sleep Phase Syndrome which is a circadian rhythm disorder. In general those things are very genetic so we tend to see them from a very early age. Whereas insomnia is much more behavioural and environmental and so it can trigger at any age.