That is an unlisted vent termination which is a fire hazard and should be removed. You need to identify the make, model and serial number of this fireplace and venting. Get the listed instructions, then install to those instructions and the building code.

The IRC, section R1003.20 calls for crickets when the chimney is >30 inches, which they reference as parallel to the ridgeline. While this is hip, since it is greater than 30", it should have a cricket. Due to the proximity to the ridge, extending the ridge would have addressed it properly. Even thought R1003 pertains to masonry chimneys, most AHJs will apply it to chases as well. R905.2.8.3 does pick it up under roof assemblies but they still refer to it as a "chimney".

I suggest you recommend a Certified Fireplace Inspector perform a Level II inspection of this unit ASAP. Click on the Fire Service button to locate the one nearest you.

HTH,
Bob

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