Check https://www.reddit.com/r/kustom/comments/fm23a0/are_null_empty_valuesif_conditions_bugged/ for more info.
In short:
1) conditions seem to be read as a whole, even if the first part of an "and" already fails. if(0 and 1) should stop at 0
2) null/empty string values used incorrectly in e.g. subtraction operation because of 1) cause the whole condition to always be "true"