There are reported issues with IMGBB.

Lately, about one out of ten completely refuses to go any farther than watching the spinning wheel forever; I click "Upload"; it goes through the motions and then says 100% uploaded; but, the little wheel is still spinning and nothing has been loaded.

Once it starts this on a particular image, no amount of retrying will do any better.

Sometimes, changing folders works; sometimes switching to another image and then coming back will work.

For my most recent image upload, I tried my whole bag of tricks with no success; it would act as if everything was working right up to the last and then the little wheel would just keep spinning and spinning.

I finally walked away and left the wheel spinning while I did something else for about 90 minutes and still no go; the wheel was still spinning.

To finally get this particular image to upload, I stripped the name and all metadata, gave it a completely new name, moved it to a different folder, opened PSE&More in a new window and it worked.

Stripping the metadata must have been the key to this as doing everything else without deleting the metadata did not work.

The puzzling thing about it is, I had already successfully uploaded other images from the same folder, with identical metadata save for the timestamp, and they all worked without hesitation.

I'm not sure why those changes worked. Possibly a browser issue of some kind. Have you cleared your cache or tried another browser (using the original image and folder)?