cloudflare tunnel uploads stuck

Hey y'all! A friend recently switched over to use cf tunnels to connect to a self-hosted nginx server. He uses Nextcloud's GUI to upload new files to that server through the tunnel. Apparently the uploads get stuck at 100% and never complete. Small files work fine, ~700KB, but larger ones tend to die. This was not an issue until he migrated to tunnels.

Any debugging suggestions or thoughts?