This is something I’ve seen often on old archtops with pickups routed into their tops. The longitudinal braces under the soundboard can come loose from years of downward pressure from the bridge. When I see what might simply be a minor neck angle issue, I typically will remove the neck pickup to see if the braces have popped loose. In this case, both braces were loose, and the top’s geometry had shifted.
So, with a syringe, wood glue is injected along the loose section of bracing, on both sides of the pick up cavity, and then clamped. For the main clamping, I use small c-clamps with a wood block backed by cork to protect the finish. I am using small adjustable clamps with soft jaws, closer to where the separation began, which requires less pressure. I could see the top actually change its geometry as the clamps were tightened, pulling the braces and top back together, as they were meant to be. The minor shift in what appeared to be a neck angle problem turned out to be, as I expected, simply a matter of stabilizing the top, and getting it back to where it belonged. The drop of water seen of the fingerboard edge was from when I was cleaning up the glue squeeze-out, and was wiped up right after this shot was taken!