What are you trying to upload from? A desktop/laptop computer or a phone/tablet? I know others have had trouble with phones. What internet browser are you using? If it has a pop-up blocker, that might be interfering.
This has come up before (see http://www.ticklingforum.com/showthread.php?324576-upload-pics) and it solved itself without me really figuring out why. I encourage you to try the following:
1) Do a cache/temporary internet files clear if you have not already
2) Try with a different browser. Vivaldi, Chrome, Opera, Edge, Safari, and so on