tmux "chord" keyboard shortcuts not being interpreted on Mac

I'm trying to use "chord" keyboard shortcuts for tmux (ctrl+b, ctrl+d to detach, ctrl+b, ctrl+[ to scroll), and they are not being interpreted.

What I've tried:

• I tried this in VS Code (remote), VS Code (local) and my local terminal and it didn't work in any of them, so I believe this is a Mac or a tmux issue.
• This seems random - it worked up until a few hours ago and suddenly stopped. I'm thinking I accidentally changed some setting or received some mac update. But I don't recall either of those things happening.
• I tried reinstalling tmux, reinstalling vs code, updating Mac.
• The VS Code terminal.integrated.allowChords setting is set to "True"
• My cursor disappears after the "ctrl+b" step when the terminal is focused. If I try doing this command when, e.g. a browser window is focused, the cursor does not disappear.
• If I use this in a normal terminal (outside tmux), ctrl+b does nothing, then ctrl+d deletes a character. But inside tmux, ctrl+b does nothing, then ctrl+d also does nothing. So it seems like the command is getting captured somehow.

Other chord commands work (e.g. cmd+shift+t to open recently closed tab).

What might be causing this issue?

Writing the full tmux settings to ~/.tmux.conf as described here solved this:

tmux show -g > ~/.tmux.conf