When returning to Caer Lem more than once you cannot proceed past the moving bridge because it does not reset.
Version 1.0.22 - Public - e
Create a new Save
Complete the story through Caer Lem and the subsequent return to Caer Cyflen
Return to Caer Lem and complete the area, including exiting the rear tunnel
*Return to Caer Cyflen and pick up the Side Quest "Sorak Relic"
Return to Caer Lem and enter the back tunnel. You can proceed to the moving bridge, but it is facing away from the party and cannot be turned. Even abilities such as Fly do not give access to the second portion of the tunnel.
*This step probably isn't necessary, but I did so and it prompted me finding the bug.