CTRL + [ shortcut has stopped working

Help me… I have a file that I inherited that is a million years old, but my boss is committed to keeping the same file, same format, just rolling it over year after year after year. As such, there are formula names, references, hidden tabs, all sorts of junk that are clogging up the file and causing me all sorts of issues. I’m muddling through and fixing what I can, but this new issue is a real pain that I need solved asap.

The file has stopped letting me use the CTRL + [ shortcut to go to the source cell - this is now bringing me to the last tab of the workbook.

The F5 shortcut to return to the original cell is also no longer working.

I don’t have the time right now to rebuild this file from scratch, so I’m hoping someone on here knows more about this issue than I do.

Help me r/excel. You’re my only hope.