corrupted ods file

I had a .ods spreadsheet on a thumbdrive. Last time I tried to save it, LibreOffice said the file was corrupted. Since then, I tried to open it once but it opens in LibreOffice writer and all I can see are some glyphs.
The size of the file is about the same as the size of the file of the last back-up (unfortunately this was about a month ago).
Then I copied it:
I tried to unzip it, but the produced file does not look like an xml file.
I tried to open it under MS Excel, but the result was the same as with LO.

Auto-backup was not enabled and my last backup was about one month ago.

Please edit the question to indicate platform and LO version. Thanks.

I had a .ods spreadsheet on a thumbdrive.

Avoid saving directly to USB devices. They are known to have problems in general and are designed for data portability rather than as a HDD replacement. GNU/Linux has revealed a problem with the polling of USB devices. Try repeating the problem by saving to the local HDD.

Thanks for your answer… sometimes it’s just easier to edit the files on a thumb drive…