Re: Missing Bookmarks
Which version of @Voice app did you use? And are you opening exactly the same ebook files on which you placed bookmarks? Also, did you uninstall/reinstall @Voice at any time between making the bookmarks and their disappearance? Or did you go into Android system settings - Apps, selected @Voice and and executed "clear storage" function? Both uninstall/reinstall or clear storage would delete all the files and other data the app had saved.
It could be also that some system storage cleaning app or component deleted the files saved by @Voice app to "clear junk" and give you more free space. If you are aware of any such "cleaning" going on your device, you should configure it to leave @Voice app folder intact.
What you could do, but I don't see much hope: find a good File Explorer app (e.g. ES File Explorer from Google Play), set in in its settings to show also hidden files and folders. Then navigate with the file explorer to @Voice folder app (usually something like /storage/emulated/0/Android/data/com.hyperionics.avar/files) and enter the directory named .config there. See if there are any files there with names ending with .bmk. If you find such files, copy them also first to e.g. download directory to have a backup copies. Then click each of these files and open it as a plain text file. The 2nd line in each of them will have the original file name of an ebook, document or other article for which these bookmarks were created. Let me know if there are any bookmark files there for the ebooks, that you want to recover. Most probably these files were deleted somehow though.