Weird Jellyfin/Streamyfin/Swiftfin + Reverse Proxy + Cloudflare Problem

[nothingveryobvious]

Hi all, I'm having a weird problem with Jellyfin clients on my iPhone. For my server, I use it with SWAG reverse proxy and Cloudflare DDNS. Cloudflare is set to use DNS only, no proxy. The following apps are all on my iPhone, accessing my Jellyfin server at https://jellyfin.mydomain.com

Jellyfin:
- WiFi at Home: Can populate libraries and play content
- WiFi Somewhere Else: Can populate libraries and play content
- Cell Data: Can populate libraries and play content

Streamyfin & Swiftfin:
- WiFi at Home: Can populate libraries and play content
- WiFi Somewhere Else: Can only populate libraries; cannot play content
- Cell Data: Can only populate libraries; cannot play content

Does anyone know what’s going on here? I can’t wrap my head around it. Is the Jellyfin app doing something differently? I’d greatly appreciate any advice. Thank you!