Chat skips a block of messages when someone posts while you're catching up on unread history

awesomerobot · November 3, 2026, 11:40pm

Thanks for the report! I could repro using your steps and that certainly isn’t ideal.

I’ve added a fix here:

FIX: Don't skip chat messages when a new message arrives while reading back (#45528)

main ← fix/chat-load-more-flag-clobbering

awesomerobot

11:40PM - 03 Nov 26 UTC

+783 -49

Reported in: https://meta.discourse.org/t/chat-skips-a-block-of-messages-when-so…meone-posts-while-youre-catching-up-on-unread-history/416446 When you're scrolled up in the chat history and newer messages haven't been loaded yet, a new message that comes in is added to the end of the partially loaded list. The next page is then requested from that message. Because of this, everything between the most recent message you had loaded and the new message is skipped and marked as read, and doesn't show up until you reload the channel. Loading older messages also reset `canLoadMoreFuture` to `null`, which broke the "new messages below" arrow. This change makes `ChatMessagesLoader` request the next page from the oldest and newest messages the server has sent, rather than from the ends of what's on screen, so live messages can no longer change where pagination starts. It also only updates the flag for the direction it fetched, so the arrow keeps working. While newer history is still unloaded, live messages are now counted on the arrow instead of being added to the list, so they appear in order as you scroll instead of pages loading in above them. If one arrives just after the server built the last page, the loader fetches one more page so it isn't missed. Before... note the new message and our count ending at 55 of 96 https://github.com/user-attachments/assets/b6424498-c158-4410-81d2-717c440d5bb7 After... we see up to 96 and the new message https://github.com/user-attachments/assets/572153dd-52e2-49f3-b3da-bae740c8757a

This will be available with Discourse updates soon.

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Chat skips a block of messages when someone posts while you're catching up on unread history

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