[Accordion] Panel exit animation is sometimes skipped

[joncoronel]

Bug report

Current behavior

Panel exit animations sometimes get interrupted due to display: none being applied prematurely to the panel that is going from opened state to close state. Specifically when multiple={false} and transitioning from one opened panel to another panel being opened. This causes the height animation to be skipped so there's a sudden layout shift. Hard to debug since it's very inconsistent. It seems to occur more often the more complex the content in the panel is.

FocuSee.Project.2025-10-29.22-42-44.mp4

In the video, when the top most trigger is clicked, the previously opened panel immediately is hidden instead of transitioning out.

Expected behavior

When alternating opened panels, the previously opened panel's height should transition it's height to 0 while the newly opened panel should simultaneously transition it's height to the content of the panel.

Reproducible example

CodeSandbox

Might require opening different accordion panels for a bit for the issue to occur.

The video taken was of this example. I duplicated the select component in the panel as it seems to make the issue occur more often.

Here is a minimal repo as well with essentially the same code and issue: https://github.com/joncoronel/base-ui-accordion-bug

Base UI version

1.0.0-beta.4

Which browser are you using?

Chrome. Does not occur in Firefox.

Which OS are you using?

Windows 11

[atomiks]

There was a fix for collapsible/accordion animation behavior recently, but it's not released yet (#2985)

Does the issue reproduce for you using a preview release of the latest master commit? https://codesandbox.io/p/sandbox/base-ui-accordion-animation-bug-forked-lny58v (I can't see the issue in your CodeSandbox either, though)

[joncoronel]

Yes I can still reproduce it in your CodeSandbox. Try opening the preview url for your codesandbox in its own tab and just randomly open different panels. It should occur often enough. Only on chrome btw.

[atomiks]

Yeah, I can see it. It's kind of hard to catch if the animation is fast, but I can see it when recording the screen and going frame-by-frame when it happens

[joncoronel]

Yeah it's more apparent when using it in a more realistic scenario where there may be more content underneath the accordion which causes all that content to quickly shift up. I had tested setting the transition duration to something long to see what's happening and display: none was being applied too quickly. I enabled keepMounted and the issue still occured so doesn't seem to be caused by that.

[atomiks]

@joncoronel try out the sandbox linked in #3101, I haven't been able to reproduce it, but it's pretty hard to begin with

[joncoronel]

The sandbox link seems to be broken or I don't have access to it?