Hello I am using Excel on Mac (365 subscription) and having a frustrating problem here: the data I have entered and saved in the file disappeared, any idea why?

It has happened once recently and I thought "okay...maybe it was me who forgot to press save", so I re-entered the data (so much!!!) again and saved it nearly every second. Unfortunately when I opened the file now, the data is all gone again.......................
Is there any reason why this is happening, or if it is something about the subscription? (I am signed in all the time.) Seriously this is extremely inconvenient and annoying.

Thank you in advance!