Grey Covers - returning problem

[Popsinator]

Originally had this problem with my NC and now it's randomly occuring on my NT - on some sideloaded content, the cover art won't show up in my library, I get the infamous grey cover. I've always used Calibre to manage my content, and in > 99% of the time, I have no cover issues. When converting the ePub via Calibre doesn't work, I open the book in Sigil and save it; In the past that did the trick however it's not working now.

I've looked at the books that are problematic and cannot see any common threads that might be the culprit, I'm running the latest version of Calibre and have it properly configured to handle conversions for my NT. On the last transfer I had 34 books I was adding to my NT, 17 of them had cover issues. Does anyone have a recommendation for something else to try? 

[CascaraBorzoi]

I had that trouble when I first started using Calibre...I solved it by loading one book at a time, rather than a group together.

Since I started loading one at a time, I have had absolutely no problems with the covers.

[deemure]

Using sigil is not always going to solve this problem. In fact, it can cause it. If you have not done so, in calibre re-add the cover image in the metadata section even if the image is shown there before converting epub to epub. It may be that the cover's jpeg image has the extension .JPG which I know in the past has been unreadable by android. You may want to check this as well and change it to .jpg.