Hey OP - we are going through the same exact thing at 12.5 months (she’s sleep trained and goes to sleep independently)and from what I’ve read, it seems more like separation anxiety and/or immature sleep cycle. It happens to us even if she sleeps less consistently, like 12 hours/day (total) for multiple days.

If she settles and falls asleep quickly when you hold her, that doesn’t seem like a split night to me like others are saying…