See attached file.
With this selection it now stops for me at 6450/31122 images, I think it initially stopped at 6492 or so before I tried to restart it.
Originally it halted at earlier zoom levels too:
9,25,56 images - no problems
169 images, stops at 111, then stops at 100 at every retry.
552 images, stops at 247, then stops at 200 at every retry.
2068 images, stops at 743, then stops at 700 at every retry.
5850 images, stops at 58??, then stops at 5850 at every retry.
After having tried some other ways to get to the data, mostly using path tool to "paint" the desired area in paths, without selecting too much off-shore area, it seems it can now get past the earlier stall points.
I am not sure that my theory from the first post is correct, it is just the only cause I can think of.