Good catch! The old diesel-foil cats would warp longitudinally, as well as shrivel slightly, so that they didn't fit well in the Woodstocks' two-piece cast iron cat frame. I was able to flatten them somewhat, then wrap with enough interam gasket to prevent leaking. I never called in the warranty on one, just patched 'em together and got 'em to work.
With an open gap, smoke would blow right around the edges. If you went out to look at your stack, you might well assume that the cat was shot. Not sure how the cat is set up on the PH, if
@Berner may have had a cast cat frame in his stove. The new DuraFoil cats don't use the frame or interam gasket. They have two tab ears with bolt holes, and you just bolt the cat in using the old shipping bolts that kept the ceramic cats from breaking in transit (in the Fireview and Keystone.)