If the account was inactive for a long time and then logging occurred from a different browser and from a different IP, then the exchange often blocks such accounts when sudden financial activity occurs on them. I wrote about this in my notes on using centralized exchanges:
No, I log into the account from time to time, I haven't made a deposit for about two months, but everything is done through a dedicated IP, saving cookies, a clean operating system and a browser that I only use to access that account, so it's not a security problem.