Matterbridge is unable to fetch any media from pantalaimon

[Kimapr]

Pantalaimon version: 0.10.5
Matterbridge version: 1.26.0 6dafebc

I'm using matterbridge to bridge an encrypted matrix room to a private IRC room, with pantalaimon in between the matrix homeserver and matterbridge. The bridge is able to transfer text messages back and forth just fine, but whenever someone sends a media file on the matrix side, the IRC side receives a broken file from matterbridge's mediaserver with this content:

{"errcode":"M_UNKNOWN","error":"invalid server ID","mr_errcode":"M_BAD_REQUEST"}

instead of expected content. This only happens with encrypted media, plaintext media is successfully transferred over to the IRC side.