Thanks, Janice, I got the information.
Do you have a staging site that I can use to investigate? If not, would you mind if I cloned your site onto my own staging area?
I suspect that simply changing the priority of the init action would fix it, but I’d really like to know what it is that’s causing the conflict.
add_action( 'init', array( $this, 'init' ), PHP_INT_MAX );