If your LO had a sleep regression around 2 years, what was it like & how long did it last?/

Both of our boys have been having sleep issues and I have no idea what else to try. A couple months ago, E (and F to a lesser degree) started taking a couple hours to fall asleep or he would wake up in the middle of the night and just be awake for 2 hours or so. Our pedi recommended using melatonin for a few weeks to help get his circadian rhythm back on track. It was great while they were taking it. They were actually sleep at bedtime and would go to sleep within minutes and sleep all night. After 4 weeks, we needed to stop giving it to them per our pedi's instructions and their sleep was awful again from the first night. They don't go to sleep until between 9:30-10:30 no matter what time we put them to sleep. This happens whether they played hard outside all day or had a quieter day. Naps were really awful for a while, but those are actually getting better. I don't let them sleep longer than 2-2 1/2 hours and and wake them up by 2:30 at the latest so I don't think their naps are impacting their night time sleep.

So . . . I'm curious what other people's experiences have been with 2-year sleep regressions.