Inaccessible voice memo
The paid app iExplorer can show Voice Memos in a Finder-like interface. iExplorer has a free trial which will allow you to verify if the Voice Memo exists as a file on your iPhone. You will need to purchase the app to download the memo file.
Disclaimer: I'm a highly satisfied user of iExplorer and I'm not connected with Macroplant LLC financially or otherwise.