I have two sites which haven't been changed for a week or so. Then this error message began to pop up out of nowhere. I was led to believe it was due to a custom web part, since I have a couple on my page from the SP app store. I removed them and deleted my history and cache, but the message continues to pop up. It also only pops up on the main page of both of my sites. None of my subsites or added pages have it. Could this be related to my Microsoft license with my company's IT department or something?