The issue here is both of the "word-order kind" and "of the particle kind".
*問題は私が作りました [が, objective, BUT subject of the action] = (the problem/question-objective) (I-subjective) + verb: made.
1-Just as reminder: the ga particle indicates a subject among other possible subjects. Thus, in this case, it means "I, among the others"
2- 問題は is put in the first place as grammatical subject, this means that it is not a "general problem/question" but something definite which is already displayed or put under attention.
The translation will be: "I was the one who made THE problem." or "That very problem was made by me"
*私は問題を作りました [は subjective] is a straight sentence S+O+V, which puts emphasis on the action and not on the detail. The listeners are not aware of what kind of problem came up, just that I "made" one.
The translation is simply: "I made a problem/question (nuance: and that´s what happened)"
With 問題 you might also use 提起する (as "to raise a question/problem").