Not only do I not have trouble in OO, I uploaded the sheet to Google Sheets and had no trouble.
As I said, there is no format assigned to A and B, or most other columns except where I set it to something numerical because I wanted a specific output (e.g. currency, no decimal place)
I attempted to format A-E & H simultaneously to "text". Excel crashed and reloaded itself.
I attempted to format ONLY A. Crashed, didn't reload. Same happened with column B.
I attempted to copy the CONTENTS ("BlackNoise") of cell 123A. After pressing enter, it crashed.
I do not have any data entry error rules set up as I haven't learned how to use them. In fact, I don't have any rules set up at all for the entire file that I can recall.
The only thing that has actually changed is that I switched from an old Dell keyboard to a Rosewill RGB that I just bought. I switched back to the Dell and tried to overwrite 123A by typing in the same thing. Crash!
Previously, please note, 123 was not a problem.
When I attempted to paste the sheet into an empty sheet...Well, you can guess.