Just bought Hero 9 Lens mod and it arrived today, has the same problem as described. The problem is incomplete machining of the bayonet mount ring during the manufacturing process. The bayonet lock ring is on the Lens Mod, the bayonet tabs (2) on camera fit into the bayonet ring then you rotate Lens Mod one quarter turn clockwise to full lock position resulting in Lens Mod being squared to camera this occurs if bayonet mount ring bevel groove has been machined to the proper length. Premature lockup point occurs when as in this case the bayonet bevel groove was not cut long enough resulting premature lockup and off kilter Lens Mod relative to topline of camera. The fix which I did, but don't recommend because of possible warranty termination, but effectively solves the problem with out causing other issues was to remove the 4 screws holding bayonet lock ring to Lens Mod and bevel off the remaining approximately 1/8 inch of metal ledge which cold stops the camera bayonet tabs from going the correct distance. Anyone who has "forced" the bayonet tabs beyond that blocking ledge which is half the height of the normal stop ledge has damaged the bayonet on one half or both halves. This damage would result in loss of water proofing, sealing when reinstalling the original protective lens which would than appear to raised up above it's normal position resulting in leakage.
I did my fix using a fine diamond filing bit in a dremel tool at moderately slow speed with excellent lighting and bayonet fixed into rubber vice jaws. Finished result was normal force used in twisting on the Lens Mod and Lens Mod square to camera topline.
I had called to return the Lens Mod, but customer service wanted me to jump through hoops, such as taking youtube video of problem and sending to them and than do a back and forth on a camera lens where anyone taking the time and using a magnifying glass could view the bayonet mount both halves and see the unmachined blocking ledge. My choice was do it myself, but I suggest others return it for one correctly manufactured, keep doing it until they send a good one.
