We had this same issue. Couldn't reliably duplicate it for a bug report, though. For a few sessions, it only happened to me. Gradually, it infected others, too, until everyone had it happen at least once.
The weirdest part was if you activated it, it would transition, but still be "up". Activate again, transition, still "up". Usually the 3rd transition would make it by physically "down", but it would still appear to be up. You'd step across thin air, then phase through the bridge model to get inside. Appearance and physical model wouldn't be in sync. Super weird. We just ripped it out and jump the gap now.