app.element.io on matrix.org fails to load attachments

[nt8r]

Steps to reproduce

1. Where are you starting? What can you see?

I'm logged into matrix.org via SSO from github.com. In every channel (such as #main:postmarketos.org, aka #postmarketos:matrix.org, but I see this everywhere) attachments fail to load. Image previews just show a spinner, and other attachments do nothing when clicked on.

2. What do you click?
   Image previews (which are missing, just showing spinners) or attachment download buttons.

Outcome

What did you expect?

The attachments to show previews and download when I click the download button.

What happened instead?

Previews never show up; when clicking the download button, an error box pops up saying (for example):

Download failed

An error occurred while downloading this file
M_NOT_FOUND: MatrixError: [404] Not found (https://matrix-client.matrix.org/_matrix/media/v3/download/matrix.org/rClrxSFSsjJgaovxRCTZmheM?allow_redirect=true)

If I middle-click images, I get a page like https://matrix-client.matrix.org/_matrix/media/v3/download/matrix.org/rClrxSFSsjJgaovxRCTZmheM?allow_redirect=true with the contents:

{"errcode":"M_NOT_FOUND","error":"Not found"}

Operating system

Arch Linux

Browser information

Firefox 138.0

URL for webapp

https://app.element.io/

Application version

Element version: 1.11.98
Crypto version: Rust SDK 0.10.0 (3cc301d), Vodozemac 0.9.0

Homeserver

postmarketos.org and/or matrix.org (I'm not sure how to determine which is more relevant in this case, channels seem to be bridged/aliased)

Will you send logs?

Yes

[nt8r]

Follow-up to #29398, logs sent.

[nt8r]

Clicking "view source" on an event that doesn't load shows something like this:

{
  "content": {
    "body": "Screenshot_20250430_105024.png",
    "info": {
      "h": 2106,
      "mimetype": "image/png",
      "org.matrix.msc4230.is_animated": false,
      "size": 2787651,
      "thumbnail_info": {
        "h": 600,
        "mimetype": "image/png",
        "size": 342406,
        "w": 307
      },
      "thumbnail_url": "mxc://matrix.org/aOnSlUXRPdBVUWnBQnaXanfy",
      "w": 1080,
      "xyz.amorgan.blurhash": "T8E3k%}_00EwsEVt009Et7=}NF%f"
    },
    "m.mentions": {},
    "msgtype": "m.image",
    "url": "mxc://matrix.org/rClrxSFSsjJgaovxRCTZmheM"
  },
  "origin_server_ts": 1745967250735,
  "room_id": "!xgUMIsYnSIXklwbhrG:postmarketos.org",
  "sender": "@reallyrealaccount:matrix.org",
  "type": "m.room.message",
  "unsigned": {
    "membership": "join",
    "age": 84115026
  },
  "event_id": "$eViGerWuMFysDlmPYYLv48pXw-89gW88vIkR5-7X8XQ",
  "user_id": "@reallyrealaccount:matrix.org",
  "age": 84115026
}

[MidhunSureshR]

I think the service worker is failing to do its thing. What do you see in the inspector? https://firefox-source-docs.mozilla.org/devtools-user/application/service_workers/index.html#debugging-your-service-worker