I notice that when I'm mining an ore, the progress bar gets to almost 100%, and then I get my ore. Shortly after, it goes back to zero.
That's not what I would expect. Instead, I would expect that I would get my ore at the same time as the progress bar goes back down to a low level - the ore arriving when the progress bar passes from 100% to zero.
So it seems the progress bar is slightly lagging behind my actual progress.