Some Computers Won’t Submit Form

Hello,

I am currently having an issue with a contact form I have setup on one of my work’s websites.
The form currently has the normal text fields, radio buttons, etc. along with a few file uploads at the end so users can attach images or documents (it is a request form we are implementing through one of our secondary websites).
On my computer, I am able to attach any file I have specified without any issues, but my coworker who sits across from me in the same office cannot upload the same files.
The main contributing factor to this issue seems to be when he tries to upload an Excel document.
I know I have it specified in the file restrictions because I can upload it from my computer, and there are a couple others in our office space that can, too. But for some reason, it does not work at all on his computer. If he submits the form without any files attached it works fine, but the second he attaches an Excel document, it does not submit. This is how my file upload looks on the backend:
[file file-upload-1 filetypes:pdf|jpg|jpeg|png|gif|xls|xlsx|docx limit:20mb]
I am able to upload any file from this list, but my coworker is not able to, even though he is literally 10 feet away on the same network as me. We also made sure the file size does not exceed the limit, and his size is under 20mb.

If you have any feedback for me, it would be much appreciated. Thank you.