Sleep training going backwards

We sleep trained our 5mo last month. We had great success initially. Within a matter of days, she was putting herself to sleep at bedtime from awake in her crib within 5-15 mins each night with minimal crying/fussing (some nights seeing no crying at all!). She also went down to 1-2 wakes a night, sleeping through to 5am a lot of nights. As she was only 4 months when ST, I didn’t want to night wean and so I followed the 5/3/3 rule.

However, the past week or so we have seen a real regression. She is now crying or screaming a lot when put down (sometimes for longer than 10-15 mins) and she is also waking a lot more during the night, sometimes 4-5 times.

I’m not sure what has gone wrong. She has been showing true signs of teething (dribbling, unsettled in day etc) so I’ve applied gel and medicated where I feel appropriate. But today, she was super happy all day with no signs of teething but has screamed so much when put down.

Wake windows are 2/2.5/2.5/2.5 and she is 5 and a half months old. Her daily nap total is usually 3-3.5 hours, DWT is 7am and bedtime is usually around 7.15pm

EDIT to add: we have not nap trained yet. She is still either fed or rocked to sleep for naps or has carrier/pram naps