The phrase "problem with formula" is an idiomatic expression that refers to a situation where something is not working or functioning correctly. Full definition
If your baby is having a real problem with her formula, then choosing another type of baby formula can be important. (verywellfamily.com)
There are about 13,000 studies showing problems with formula - feeding, so why haven't you heard any of this before? (normalfed.com)
The South African mining giant, needless to say, has a vested interest in promoting this «rule,» and there are obvious problems with the formula. (moneysense.ca)