missing formulas in Excel

Hello

i transferred a CSV file to work on, made changes and all good. Saved it and today the formulas are missing  - values are there and correct but no visible formulas.

any idea how to restore the formulas that are there but hidden?

i have copied the worksheet and tested if i can use it and i can and when i write a new formula in the existing cells it shows it for that cell as it did yesterday.

I have contacted Microsoft and they suggested here

Thanks

Wayne