Bridged profile avatars are not redownloaded/reuploaded after purging the media database or deleting the media files

This issue was originally created by @Xinayder at https://github.com/matrix-org/dendrite/issues/3179.

Background information

Dendrite version or git SHA: v0.13.1
SQLite3 or Postgres?: Postgres 15
Running in Docker?: No
go version: 1.20.2
Client used (if applicable): Element

Description

What is the problem: Avatars from bridged users are still pointing to old URLs and MXIDs even after deleting the media files and purging the mediaapi database, falling back to the default text initials avatar
Who is affected: Clients
How is this bug manifesting:
When did this first appear: After deleting the Dendrite media folder on the server

Steps to reproduce

Delete the media folder used by Dendrite
Restart Dendrite
Avatars will now be missing and Dendrite won't redownload them. (expected, as the media files no longer exist)
Purge the mediaapi_media_repository table
Restart Dendrite
Avatars will still be missing

I run a local Matrix instance using Dendrite and I host a few Mautrix bridges for Instagram, Messenger and WhatsApp. If I understood correctly, the profiles are created locally on the homeserver, but after deleting the media folder, the avatars are not found, which is expected. However, even after deleting the mediaapi table, the avatars are still pointing to files that no longer exist.

The only way avatars get updated is if the social media profile updates their avatar on the respective social media.

Dendrite should try to redownload the avatars if they point to nonexistent media files.

element-hq / dendrite