LO Calc file - Data and tabs missing & turned into a single line of Unicode characters

Hi there,

Hoping someone out there would be of LO Calc assistance fingers crossed

I had a normal Calc document filled with data and multiple tabs. However, when trying to re-open said file, a Text Import dialog box now appears, and data is now replaced with a single line of Unicode characters.
File size looks to have dramatically decreased and last modified date looks unfamiliar (a date that I was not working on document).

Is there a way to correct or restore previous file?

Unfortunately, there does not appear to be a back-up saved in LO ‘Backups’ pathway.
File > Versions button is also greyed out.

Defintely a lesson for saving a copy of master files!

Thank you in advance!