Hi @Cooke, Adam ,
I'm glad to hear you solve the problem ,if you have any issue about SharePoint, you are welcome to raise a ticket in this forum.
By the way, since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others.". and according to the scenario introduced here: Answering your own questions on Microsoft Q&A, I would make a brief summary of this thread:
[SharePoint List .zip Attachment not showing]
Issue Symptom:
I'm trying to upload a .zip file that's about 80Mb as an attachement to a list item. I've tried several times with changes to other attachements (removing them so there is only one other) and changes to the .zip file name in case there are issues I'm not aware of. No luck.
Current status:
Eventually the List just worked itself out.
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