Dynamics CRM on-prem weird issue: Option missing from option select field customisation but visible otherwise

Hi all,

I've encountered a strange issue and I was hoping someone here could help me with it:
In our CRM, on contacts we have added an option select.
This select has 9 options, but two of them are very similar - the only difference is one has a "-" in the name where the other has a "–".
This is confusing and pointless so I went to remove one from the customisation screen, but when I edit the option select I can't see one of the options.
Specifically, the one with the "–".
I'd like to remove this option to avoid confusion.
Any ideas?

Regards,
Nick