A client of mine was having a similar issue. After talking with them, it turns out there were two things going on:
there were travelling in Europe, so their internet connection was changing. Some places it was slow, other places it was speedier…this threw me off a bit until I thought about it, since sometimes things would sort of work and other times it would not. the speed of their internet of course being the variable factor.
the other thing was that they were taking piles of huge-resolution photos, and then trying to load several of those monster-files at once. However, other times they would take smaller-resolution photos from their phones and upload them and have no problem.
Given those two things, and the fact that they did not have a grasp on photo-sizes and resolutions…they were just frustrated when things were not “working”
I had to give a lengthy tutorial on how to re-size photos to more web-friendly proportions. Once they grasped the concept, they no longer had any problems.
Not that this is what the two here were dealing with, but just as a first-thought.