Same for me recently. Now that Instagram IS Facebook, maybe Facebook doesn't make a difference between fake Instagram accounts and fake Facebook accounts in the report ?

I have both fake Facebook accounts and Instagram accounts (like 3 or 5), and Instagram deactivated a recent account I created for "suspicious activities". I only liked one picture of an actual person and sent one private message with that account... Meanwhile, my other 4 Instagram accounts and Facebook accounts are fine, even if I sent and liked total garbage