Hm, the only thing I can think of is if maybe the images showed up in the album (which they do before they've actually been uploaded to imgur's servers), and perhaps you navigated away from the page before the upload was finished. Since the 250 box challenge involves a lot of separate pages, I can imagine the upload might have taken a while.

Honestly though I'm not sure. I do know imgur can have various issues, but I suppose the first thing to pin down is what kind of device were you trying to upload them on? And also, is it possible for you to try uploading them to another imgur album?

Honestly if imgur is too much trouble, then anything else - dropbox, google photos, google drive, etc. - are also acceptable.

I had the same problem with the 250 box challenge. No matter what I did Imgur did not keep all the images. A few days later I tried another submission and it worked. I don't remember which I did but I either dragged the images onto the Imgur submission window or I added each individual image using the add another image button. I think I dragged them from explorer onto the submission page. Hope that helps.

hmmm, i usually copy the url of the website instead of clicking each link for the images, and that usually works for me. Idk if it'll work but give it a test run and see if it works, hopefully it works out okay. i usually do it on pc cuz it's a bit easier and i email the images to myself and then create a new folder with all the images that contain the assignment and then when i've recieved all photos i select all of them and then upload them to imgur, and then when everything's like uploaded and stuff i click the url of the website itself and then copy and paste it onto the submission box and then click it to see if it shows all of the images correctly or not, and it usually works out pretty good