Wake ups during first hour of night sleep (17 wk old)

Hey everyone! First time dad to a beautiful 17 week girl (will be 4 months on Friday!). Her overnight sleep was running smooth with our 830-9pm bedtime and then usually an 8 to 11 hour stretch with possibly 1 wake up where we either fed or just rocked her back to sleep.

She has unfortunately grown too long for the bassinet (we placed her horizontal and she ended up vertical and getting stuck/upset in the morning) and have transitioned her to the crib in her own room. The first night was not so great, up every 2 hours and rocked back to bed and she quickly fell asleep. 2 nights ago was better, 6 hour stretch followed with a wake up, feed, rocked back to bed until morning. Last night was similar, 6 hour stretch, wake up/feed, then back down for another 4.5 hours. The strange thing the past 2 nights is in the first hour of us putting her in the crib she would wake up once or twice and need to be claimed. It usually would happen within 10 mins or so of us transferring her to crib when she was asleep and leaving the room.

My question is, what is causing these wake ups during the first hour? We have kept everything the same (including wake windows and bedtime routine) from when she was sleeping 10 hour stretches in the bassinet. Could this just be her getting used to the space and crib or could this be an impact of the dreaded….4 month regression?