5mo waking and screaming half an hour after being put down for night

[Bumpylady]

Just that really and any advice about how to deal with it/ what is causing it? He has a bedtime routine and goes down c. 7pm but wakes after half an hour with me and DH taking turns to settle him until about 11pm when he eventually conks out. It's driving us insane - any ideas about how we can stop this?

My LO started doing that around 4 months. The only thing that calms her is a dummy. That usually sends her back off if I catch her before it goes past the point of no return! I usually go up and take it out again after 10 mins.
As you can guess, this still happens every night and she's 9 months... Think it's just the end of a sleep cycle.