Images embedded with `attachment://` are randomly placed outside of the embed by an unprompted `Message Update` event

[aamiaa]

Description

Normally you're able to set an embed image's url to attachment://filename in order to reference an image uploaded to the same message, making it appear inside the embed.
However as of a few days ago, some of the Message Create and Message Update events will randomly receive a follow-up Message Update event, which will move the image from the embed's image field to the message's attachments field, which causes it to appear outside of the embed until client restart.

The faulty Message Update event also seems to only include the following 5 fields: attachments, embeds, channel_id, guild_id, id.

Initial Message Create

^ The image is present under the embed's image field. attachments array is empty.

Follow-up Message Update

^ The image is now in the attachments array, and no longer under the embed.

Steps to Reproduce

Send an embed with an image by utilizing the attachment:// url.
Might require multiple attempts.

Expected Behavior

Either no follow-up Message Update is received, or it contains the correct data.

Current Behavior

An incorrect follow-up Message Update is received, which moves the image from the embed to attachments.

Screenshots/Videos

DiscordCanary_fExk7ivBLy.mp4

Client and System Information

Desktop and mobile clients
Discord API v9

[Thorvarium]

I am having the same issue, this is ruining my bot.

[devsnek]

A fix is incoming