If Patches lowers you down to the giants in the Cathedral of the Deep, he will not show up to lock you into the Firelink Shrine tower until you talk to him again on the other side of the bridge in the Cathedral.

After dropping down, he will reappear in his normal attire by the lever that raises the bridge (across from where you first met him in the Catarina armor). If you climb up onto the rafters at the very top of the Cathedral before he tricks you to cross the bridge, he will not show by the bridge. Only cross the rafters after you have been tricked.He will then become a vendor in that spot until he moves to Firelink Shrine. If you meet him again on the other side of that bridge in front of Rosaria's chamber, he will apologize for tricking you, and if you refuse to forgive him you'll earn the prostration gesture and a rusted coin.

He will trick you into entering the bridge which he will then lower down to the giants. You MUST do this before lighting the bonfire at Rosaria's Bed Chamber. His spawn trigger is to open the main doors, on the left of the boss room, reload the area and then return. Unbreakable Patches can be found within the Cathedral of the Deep disguised as Siegward of Catarina. Unbreakable Patches is a NPC in Dark Souls 3.

Dark souls 3 patches location