Images not received in group chat, duplicate "Message-ID: <xxx>"s

[sbkaf]

• Sender Operating System:

  • iOS, freshly installed last week

• Receiver Operating System:

  • Desktop Linux v2.43.0
  • Android v2.43.0
  • Android v2.46.0 (Arcane)

Expected behavior

In a group chat 5 images should be sent and received completely.

Actual behavior

A group chat with >20 persons, 8 persons didn't received the 5 images. The others didn't say anything.
Only the first and the last image was received. Images in the middle are missing.

Analysis

Thunderbird shows all e-mails with all images.

Maybe the Message-IDs are the problem. Shouldn't they be the different?
Additionally -file names- are the same but the -images itself- are different.

Message-Id | In-Reply-To | attachment file name | received in Delta?
11111111   | 55555555    | aa.jpg               | yes
22222222   | 55555555    |                      |
11111111   | 11111111    | bb.jpg               | no
33333333   | 11111111    |                      |
11111111   | 11111111    | cc.jpg               | no
11111111   | 11111111    | cc.jpg               | no
11111111   | 11111111    | cc.jpg               | no
11111111   | 11111111    | cc.jpg               | no
11111111   | 11111111    | cc.jpg               | no
11111111   | 11111111    | cc.jpg               | no
11111111   | 11111111    | dd.jpg               | no
44444444   | 11111111    | ee.jpg               | yes

(IDs and filenames uniquely replaced in this table)

According to the sender 5 images should be visible. 10 different images are on the server.

Maybe it's connected to "send multiple images" dialog.

[link2xt]

Messages with the same Message-ID are treated as duplicates. We should not generate different messages with the same Message-ID. Not sure what Delta Chat iOS is doing, maybe it is reusing the same message object.