Message read status

[benmechen]

Hi, not sure if this is a bug or an issue on our side.

We have a large channel (1441 users), which our client are using as a bulletin board. They post important messages to their user base here, and would like to see how many users have viewed the message.

With smaller channels we can see the message read count just fine with the blue ticks. However, in this large channel some messages have a grey tick and no read count - however the odd thing is this doesn't always apply, sometimes the read count and status is correct.

Large channel (see grey tick):

Small channel (see blue tick and count):

Taking a look at channel.state.read I can see that users definitely have read the message, as their unread_messages is 0 and last_read is the timestamp of the latest message:

{
   "fc9c085f-a273-473a-9c7d-3988e4c9db37":{
      "last_read":"2022-08-08T22":"33":24.644Z,
      "unread_messages":0,
      "user":{
         "banned":false,
         "created_at":"2022-04-03T21:01:25.706467Z",
         "firstName":"xxxxx",
         "id":"fc9c085f-a273-473a-9c7d-3988e4c9db37",
         "image":"",
         "lastName":"xxxx",
         "last_active":"2022-04-03T21:48:45.26918Z",
         "name":"xxxx",
         "online":false,
         "role":"user",
         "updated_at":"2022-04-03T21:01:25.706467Z"
      }
   },
   ...
}

Looking into the MessageStatus source code, I can see that the tick is determined by the message.readBy property. I can't see this on the API anywhere - how and where is this calculated? It seems whatever calculation is being done does not handle large amounts of read events.