File attachment failing silently

I’m trying to upload a file attachment to a private notebook which uses secrets (not sure if those factors are relevant). It seems like the upload succeeds, but it never shows up in the panel and shows no messages or console errors. I’ve checked that the attachment is valid json (though can’t imagine that would affect things). I might be missing some detail, but nothing quite jumps out. Any suggestions would be greatly welcome!

Platform: Mac OS X
Browser: Chrome 80.0.3987.87
Extensions: Ghostery (disabled on observable)

This is the private notebook (you’re welcome to access it internally for debugging):

Kapture 2020-02-15 at 20.47.58

Oh maybe it was slow processing or I had to refresh the page. I’m not sure, but now it’s showing up: Screen Shot 2020-02-15 at 9.01.02 PM