Callback progress pausing

[futzlarson]

I am creating a zip of 5 files of this size:

18.87 MB
17.24 MB
333.11 MB
333.11 MB
1.09 MB

Which is 703.42 MB total. Every time, it gets to 40% and hangs. When I switch to the Network tab in dev tools, the Size is still increasing, despite metadata.progress being the same. It does eventually finish and create the zip file successfully, but it jumps from 40% to 100% every time which isn't a great user experience. Any idea what might be causing this? I can record a video if that would help.