Try clearing your cache and cookies. sometimes it happens because of that. if that doesn't work then you must've set your account to get automatically logged out after sometime. and some exchanges might also have this feature by default for security reasons. you know being logged in an exchange always might be ristky.
I don’t think this will work because if it is a bug then by re installing another version of the application will be able to get rid of the bugs, it could be a set up in the app as log them out after certain period of time. Or there have been many device which are logged into account and it is usually a thing by CEX apps to require you to login again for security reasons just like when their is change or attempted act of changing of password, best thing OP can do is to actually manually visit his settings or read FAQ and use the exchange support