Posts can get stuck above the "new item" button in slow mode on public timelines

[afontenot]

Steps to reproduce the problem

1. Browse one of the public timelines for a while. Click the "new item" button when there are new items. (Sorry, I don't have a 100% reliable way to reproduce this.)

Expected behaviour

The "new item" button, when present, should always be at the top.

Actual behaviour

Sometimes posts will get stuck above the button, and stay above it even after you click it.

Detailed description

Example of this happening:

My best guess is that there's some race condition in the insertion code. It's possible this is related to https://github.com/mastodon/mastodon/issues/22110, which also involves bad element insertions on timelines with slow mode.

Specifications

Mastodon 4.0.2 (mastodon.social) Firefox

[ClearlyClaire]

That one is very weird, the “new items” button is always output on top in React, it's not tied to the remaining content of the list. So I can only assume React is internally messing up here.