Open connections randomly close when using proxy

[reedspool]

Created an app (https://rcverse.recur using Server-Sent Events (mdn) and discovered that when using the proxy at www.recurse.com/domains the connection would (seemingly randomly) close. Confirmed the issue was isolated to using the proxy because it did not occur on localhost or on the original host. Switched to WebSockets and I believe the issue is still occurring.

Happy to provide more details or try to make a minimal repro, just wanted to get this out there since I've procrastinated reporting it