So, DD has been on a milk based formula since birth... Nestle GoodStart. Only thing different about it as a formula is that it is made with partially hydrolyzed whey proteins only. No casein (like Enfamil/Similac etc). It's not considered a HAF or other specialty formula.. Nestle just uses whey and likes to label it as having "comfort proteins"

Never had issues with eczema/reflux/spitting up etc.
I introduced cheese and yogurt as part of her weaning around 7/8 months of age... no issues at all with either. She eats loads of both of these things still with no issues.
I tried to wean to cow's milk at 14 months... we got as far as half formula/half milk and we had screaming/short naps/NWing/and bad gas with pulling knees up to chest.. now that I look back, she started a mild reaction at about 75% formula/25% milk...
Have reattempted to transition to milk a few times since then with same results at same 50/50 mix level, though without a reaction before that level of 50/50.
Have tried coconut milk/almond milk/and now rice milk and she isn't really fussy on them.. .likes the rice the best for sure though.
I tried a combination coconut/almond milk and got a reaction just like cow's milk after a week or so of using it for smoothies etc.... checked the label for cross contamination and it did list soy. I didn't even think to check that as I have never given her soy because of the whole phytoestrogen debate. Unsure if it was the soy that caused the issue.
This kid has zero sensitivity to any hidden dairy/soy - I have never restricted it and never had a problem.
She is also fine with milk in cooking...
Could this be a lactose issue? Her formula is not a low-lactose version so I am almost certain that isn't the case... or could this be a MPI/MSPI that she will outgrow at some point?? Or, could it just be a basic reaction to a new protein that she will adjust to if we push through for a couple of weeks?
So confused and don't know what to think anymore

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UPDATE Jan 10th.
So we have had naps that are 2 hrs each with no wakeups/faffing or anything of the sort.. just nice quiet and lovely sleep! Nights have been the same with the exception of tonight - took ages to settle and was quite faffy for the first 30 mins after she did settle to sleep... there is some 2 yr molar movement though so it could be a bit of that... and a bit of OT (those same teeth are causing bubs to eat half of what she typically eats in a day so we wake up STARVING at 530/6am)... makes for long days and OT to start a bit...
I just need some BW vibes that it isn't the milk, it's the teeth.