I’m having the exact same issue! Any luck solving it?
The download cloud images randomly turning yellow and refusing to download unless you get lucky coming back is a long-standing issue. It seems to happen especially often after scrolling, i.e. when you have to scroll down the list of episodes past the ones already downloaded. I can download the first page, leave and come back, reverse the order of episodes then download the new first page, but the episodes in the middle are a crapshoot.
Now that I just downloaded a lot of episodes from different series the app crashes on launch