You should get one pong for the node itself and max 6 additional pongs from the pong cache for each additional hop your ping message would travel.
So max. 7 pongs each with the MsgId of the Pong you send.

Otherwise these pongs are likely not originating from Phex, just routed through Phex.

Of course there could also be a bug somewhere, but that would require more details from you. Message dumps and if possible test cases...

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