Lots of questions? I only spotted one! Yes ime it's was mainly down to developmental stuff but for us an element of OT. R responds to OT in one of two ways usually. Either monster like behaviour and a seeming separation anxiety and sleep time or secondly goes to bed like an Angel child and is so OT, she'll just keep chatting and end up waking earlier than she Normally would, ending up with a 10/10.5h night ( which for her is short)
Advice? Don't try and work it out, it will drive you around the bend. Easier said than done when you're in the middle of it, but having btdt, I can say it!!! Stick as closely up your rotine as he will allow and manage the OT the best you can along the way.
Hth xx