Hi Jonathan,
Please provide us the information below for our investigation:
- The Office version. You can go to Excel > About Excel to check it. For example, 15.41.
- The OS version. Are you using 10.12.6 or High Sierra 10.13?
- When did the issue happen? Was there anything changed before that?
- Does the issue happen to all workbooks (even a new created one)?
Thanks,
Rena