I realise this is a time for sleep 'regression' normally. But this seems like something different. My almost 18 month old's father and I separated in September 2016. We have a biaotaiton schedule set and my son sleeps home with me primarily with one or 2 overnights with dad, depending on the week. Dad says he pretty much always sleeps all night long til about 7:30/8 a.m. when he is with him. For the last month my son wakes up wabyong bottles multiple times a night and then around 4 or 5 wakes up and cries and cries till I pick him up. It is exhausting and frustrating. Sometimes I just lay him in bed with me, get another bottle...whatever I can to get some rest. I'm beyond frustrated about this. Why is it that he sleeps totally fine at dads and not home with me.
Is that a typo? You can edit your post to reflect answers or to make corrections. Welcome to Parenting SE.
IF you are certain that your ex is telling the truth or not just able to sleep through the noise, then my best guess is that your little boy is having trouble with the changes to routine. I am thinking that regardless of whether your ex is being truthful, the little guy is protesting the change.
He may have some separation anxiety. You are the primary caregiver and your little guy doesn't have the words to express his concerns.
It's normal but distressing, and might be exacerbated by your situation. There's quite a bit of literature out there and your child's doctor may have some information.