After updating to macOS 27.2, clicking the conversation disclosure button in the message list no longer expands collapsed conversations. This issue occurs across all of my email accounts.
The behavior is as follows:
- Clicking the disclosure button on a collapsed conversation does not expand it.
- Clicking the same button on an expanded conversation successfully collapses it.
- View > Expand All Conversations and View > Collapse All Conversations both work correctly.
- The Right Arrow key expands the selected conversation, and the Left Arrow key collapses it correctly.
I have tried the following, but the issue persists:
- Turning View > Organize by Conversation off and back on.
- Quitting Mail completely using Command-Q and reopening it.
Since expanding and collapsing conversations works through both the menu commands and the keyboard, the issue appears to be related specifically to expanding conversations by clicking the disclosure button.
For now, I am using the arrow keys as a workaround.