"Is it you by any chance?"
Translation:Är det möjligtvis du?
Adverbials have three possible 'slots' in the sentence. They can go first, last, or in the so called fourth place in a main clause, see 1.1 in this topic: https://www.duolingo.com/comment/8970470
möjligtvis in this sentence is a 'satsadverbial' ('sentence adverbial') which means it modifies the whole sentence. These typically go in the fourth place. This is a question so the places get a little different, but 'möjligtvis' should go before the subject here for that reason.
You can hear things like 'Är det du möjligtvis?' in the spoken language, but that's more when people add the last word as an afterthought. It's a bit hard to make any very hard and fast rules for this, because in some cases the satsadverbial can go in other places too, but in this case you should keep it before the subject.
Typical temporal adverbials would go last, like Är det du igen? 'Is it you again?'
I do agree. I think that would be a better spot, both in english and swedish, and it logically follows that it would work the same in both. It may not be the most "formal" or "appropriate" way to say this, but it nonetheless holds the same meaning and would definitely be spoken by people