Extreme performance degradation in long-lived chats

• 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

Bug description

Please note this issue is not new. It's been occurring for over a year across Signal and iOS releases.

In any very old, large chat (eg. many messages persisting over 4-5+ years) with many gifs, stickers and media, eventually sending messages becomes a chore:

• Messages frequently take many seconds to appear after sending
• When they do appear, they have the spinning, dotted circle for an excessive amount of time before reaching the "sent" state
• Occasionally opening to a chat like this will temporarily freeze the app (no inputs register) for 10-15 seconds, then it resumes working.

This has been consistently experienced by all members in the same group chat, but also occurs in long-lived 1:1 DMs if they are old and large enough.

Archiving the old group chat and creating a new group chat proves that the fresh chat doesn't exhibit issues. However, this is not convenient to do for DMs as it would require a 2-person "group chat" with two members to constantly be recreated whenever a DM grows too large, if you prefer to preserve message history (a way to "archive" within a DM could help with this).

Furthermore, please note that I'm paying for Optimized Signal Storage as a last ditch effort here, and it doesn't help at all.

Steps to reproduce

• Have a massive group chat with stickers, media, gifs that has been around for 4+ years
• Try to use it normally. It's extremely consistent that it behaves poorly

Actual result:
Messages "disappear" after you send them. Many seconds later, they'll appear, but remain unsent. Later still, they'll finally send. Killing the app and returning when a message has a spinning, dotted circle tends to cause it to send immediately.

Open a notification to a chat: Some percent chance the app freezes for 10-15 seconds.

Expected result:
Messages appear immediately after you send them.
Messages transition to a single solid circle ("Sent" state) within moments.

Device info

Device: iPhone 16 Pro Max

iOS version: 26.5.2

Signal version: 8.21 (1757)

Link to debug log

I've sent many to support over the years. I can send a new one if requested.