"Unable to render message" from a bot, only in Element iOS and not other clients

[moodler]

Steps to reproduce

We have a bot that uses the matrix-nio library. It works fine on Element web, Element desktop, Fluffychat, Cinny. On Element IO (both iPhone and iPad) however, we just get this: ** Unable to render message. Please report a bug

Outcome

Element iOS:

Element web:

Cinny:

Here is the message source as an image:

Message source text:
{
"type": "m.room.message",
"sender": "@moodlebot:moodle.com",
"content": {
"msgtype": "m.notice",
"format": "org.matrix.custom.html",
"body": "I think it would be amazing if robots could take care of all the cleaning and maintenance. It would free up a lot of time for people to do other things."
},
"origin_server_ts": 1665554111724,
"unsigned": {
"age": 28983016
},
"event_id": "$8C5ZVwbp5VLCsc_BCG_ypEc1aNfLzjXITnCircWE6CY",
"room_id": "!HoguyYYqAHvInYDFtC:moodle.com"
}

Your phone model

iPhone 13, iPad 2020

Operating system version

iOS 16 beta

Application version

1.9.7 (but it's been happening for a while)

Homeserver

Synapse

Will you send logs?

No

[moodler]

is it as simple as Element iOS not being able to render that "msgtype" perhaps? I see the bot is using "m.notice" while mine are using "m.text"

[moodler]

It wasn't msgtype. it was the formatting.

Things worked again when we switched from HTML (the nio default) to plain text.

Seems to have something to do with a missing "formatting_body", which perhaps Element iOS is more strict about. Up to you if you want to fix that (I would).

In the meantime, we've also filed this pull request to nio: anoadragon453/nio-template#39

[ismailgulek]

It seems iOS client is spec-compliant on this case.