Hi Julian,
Thanks for using Microsoft products.
According to your description, we would like to suggest you refer to How to correct a #N/A error in INDEX/MATCH functions
If the issue still persists, would you mind providing the following information for our troubleshooting?
1.Could you please share your workbook without privacy with us? In this way, we could help you more accordingly. You could upload the sample without privacy to OneDrive or Google Drive and share the link in public.
Reference:
Upload and save files and folders to OneDrive
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2.Your subscription screenshot via Open Excel client>File>Account>Product Information as below. In order to protect your privacy, please help us mask your PII, such as email address. You could click this icon to upload image.
Appreciate your understanding and stay safe!
Best Regards,
Sandro