(((hugs)))
Six feeds in 24hrs is about right and my LO was waking anywhere from 0-2 times at night at 4 months and I have only recently noticed she will either not wake at all or will wake just once. I breastfeed so I am not sure how much she's taking but she takes it and doesn't use the breast as a prop and she actively sucks so I know its hunger. Her wake up times are also very random and last night she slept from 6.30pm-2am and then slept till 6am and the night before she slept from 6.30-5am and then after a feed slept till 6.30am. Three nights ago she slept without waking at all.
So to answer your question, I think for a 4mo, 2 night feeds are perfectly fine! I follow the same rule of thumb as day feeds - so when J was on 3hr feeds, if she woke at around the same mark at night, I used to feed her and when she was on 4hr feeds (which only started happening when we dropped the catnap around 5 months), if she would wake around 4+hrs, I would feed her.
With regards to the swaddle - how does she self soothe during the day? Sometimes babies start to want more freedom around this age and it might be that she doesn't like being in a swaddle anymore. I don't have any BTDT advice for weaning the swaddle as I never swaddled but I've attached a link that may give you some ideas.
Paci or Swaddle Weaning Success Stories HereAlso with regards to feeds during the day, are you cluster feeding? I used to do a feed right after catnap (say it ended at 5pm) and then do bath, bedtime routine and final feed (top up feed) around 6.30pm with 7pm bedtime. You could try doing that to see if it will help.
With regards to sleeping longer stretches before - what was her bedtime hour back then? Lots of babies go to bed a lot later and start to have an earlier bedtime when the 4th nap/catnap is gone and so the baby is going to sleep earlier and possibly why needs an extra feed at night?