I understand that may be disappointing, but that is the reason why we give out test accounts in the first place - not everyone has the same setup/method thus people get different results.
"There was a problem logging you into Instagram. Please try again soon." - when you get this error something looks fishy to Instagram. Like I mentioned in PMs, it is usually bad proxy/IP or flagged device/browser/bot. This could also mean account itself is flagged but I've logged in to it successfully when we were talking yesterday so it's probably not that.