Oh gosh, we know that might seem like a bother, but it’s all well-intended. You see, Instagram is very vigilant in its lookout for fake accounts, and ask for re-authentication in an attempt to sniff out these spammers. If you are using a lot of third-party Instagram apps, but not that active via Instagram itself, this could pop up.
To avoid seeing this message, we recommend using Instagram some more – this includes posting, liking and/or commenting. That should solve your problem!