Extreme lag when sending messages on long conversations

[kintonc]

• I have searched open and closed issues for duplicates
• I am submitting a bug report for existing functionality that does not work as intended
• This isn't a feature request or a discussion topic

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Bug description

There is extreme lag to send messages on conversations with long threads. This means that: after I type a message and press the "Send" button, I may need to wait 10-45+ seconds for the sent message to show up on the conversation thread. During these 10-45 seconds, the app is unresponsive.

This issue occurs on ~30-50% of sent messages. The other times, the sent messages are shown instantly on UI (which is desired behavior).

Steps to reproduce

• Find a conversation with many, many messages (at least 50k-100k+ messages).
• Open the conversation
• Attempt to send a message: type a message, and then press the Send button

Actual result: Describe here what happens after you run the steps above (i.e. the buggy behaviour)

• It will take 10-45 seconds for the sent message to show up in the thread. During this time, the UI is unresponsive

Expected result: Describe here what should happen after you run the steps above (i.e. what would be the correct behaviour)

• The sent message should appear instantly in the thread, after pressing the Send button. The UI should NOT be unresponsive.

Screenshots

Device info

Device: iPhone 14

iOS version: 26.1. Do note, however, that this issue is iOS version agnostic: on previous iOS versions (iOS 18, 17) I also have the same issue.

Signal version: 7.89. Again, this issue is Signal version agnostic, have had this issue for at least 2+ years across different Signal iOS versions.

Link to debug log

See support@signal.org email.