But I don't get why there are 2 subject
If you look closely at the grammar rather than at the logic, then il is the grammatical subject of arriver, and vous is not a subject but an indirect object. If you replace pronoun "vous" with someone's name, then the sentence would become:
"Arrive-t-il à Olivier... ?"
With this form, preposition "à" is needed, and it becomes more obvious that "Olivier" is not a grammatical subject, but an indirect object.
However, this use of the verb "arriver" is an idiom; with this idiom, "il" is a dummy subject, and "vous" or "Olivier" is the logical subject. "Il arrive à Olivier de faire quelque chose" translates to "Olivier occasionally does something".
Note the similarity in construction between French "Il arrive à Olivier de..." and English "It happens to Oliver that...". They don't have the same meaning, but they have the same construction with a dummy grammatical subject, and a grammatical indirect object used as logical subject.
As a sidenote: for automated translation, I recommend using a dedicated translation software, rather than ChatGPT. For instance, there is https://www.deepl.com/translator or https://translate.google.com/ . Both are much more suitable for the task than ChatGPT; not only are they much more reliable, but they have a dedicated user interface. They will offer alternative translations, and if you hover your mouse cursor over words of the translation or original text, they provide definitions and more explanations.