I just ran into this problem with the Processing step never completing as well, but turning on force_https did not solve it for me (using the current version of Brave in macOS 11.6 Big Sur). I worked around the problem by converting the 3.5 MB PNG image to a 524 KB JPEG.
Interestingly, the dashboard suggestion for the day was to turn on force_https, so I wasn’t perturbed to do that, but I’m guessing it wasn’t in the default instructions when my tech guy installed as well.