The only other thing that i can think of is sugar... I didnt realise that many of the cheaper and well known brands of soy and rice milk have added sugar (possibly the same with oat milk???)
Anyway we have just swapped MJ soy milk and it took a while for her to get use to it, no major issues like you have experiences, but then she only has it on her weetbix in the mornings so its not a major part of her intake.

HTH