Stickers don't appear to load

[ArrayBolt3]

Bug Description

Matrix supports the use of "stickers", which appear to be somewhat like custom emojis. I don't understand exactly how they work as I don't use them, but when others use them, I can tell when they aren't loading right, and on my Ubuntu Matrix account (@ArrayBolt3:ubuntu.com), they aren't loading right.

When stickers load right (viewing from my account @ArrayBolt3:matrix.org):

When stickers don't load right (viewing from my account @ArrayBolt3:ubuntu.com):

Notice that the stickers have been replaced with a generic image icon and a string that appears to identify what the sticker was supposed to be.

To Reproduce

Must be an Ubuntu Member to reproduce.

1. Sign into your ubuntu.com Matrix account using Element.
2. Join #ubuntu-matrix:xentonix.net (Ubuntu Matrix Project).
3. Search for the string "so the old UBPorts FluffyChat and the new one are entirely different". This will pull up a message by RAOF which contains two stickers. Neither sticker will render correctly when viewing it from the ubuntu.com account.

Environment

Kubuntu 22.04 LTS, Element Desktop installed from Element's upstream .deb package. Using a separate Element profile to sign into my ubuntu.com account as documented at https://discourse.ubuntu.com/t/synchronous-communication-with-matrix/39535.

Relevant log output

I don't know how to get logs out of Element :P

Additional context

I probably filled out this form wrong. It looks like it's intended for submitting a bug report about a server component from the server's perspective, whereas I'm reporting a bug about a server component from the client's perspective.

[ArrayBolt3]

lol, I filled out the entirely wrong form. Sigh. Sorry about that.

[kewisch]

No problem at all. I'm guessing this is some outbound request failing on the server side. Let's make sure we retry this when the federation issues are fixed.

[RAOF]

As the owner of the relevant homeserver (cooperteam.net), yeah. Stickers (or, in this case, custom emoji) are just mxc:// resources in the messages, and the problem here is likely to be the proxy rejecting connections from chat-server.ubuntu.com to matrix.cooperteam.net.