All of a sudden all my books in Adobe Digital Editions are marked "MISSING". How do I access it again?
This usually means that the location Digital Editions has listed for the eBook no longer exists. The Digital Editions Library is just a link to the eBook initially downloaded on your device. Almost always:
1. The file name changed.
2. The directory changed - the file was moved from the folder or the folder name was changed.
The default folder is My Digital Editions, usually in the Documents folder in Windows. It's possible your files are still there if you didn't move them. If you deleted this folder by accident, I hope it's in the Recycle Bin! Failing this, you will need to download your eBook again from the source vendor/store.
I have the same question; but neither of your suggestions applies in my case. I always add .acsm files to my Library using ADE and before long at least 30% go "missing" and have to be re-added. I never touch the folder path of "My Digital Editions".
Windows 10: I think you should please look into this.
I have the same problem. All the EPUB files on my computer are missing.
Books keep missing. And I have not moved any files.