I think I would need more information on octav1a's setup to make an educated guess on the problem. 
My original answer was based on the assumption that the gateway nodes simply have much higher peer counts and thus make more informed queries to the DHT. 
My question now is "Where is the file being pinned?" If at a hosting provider then my next guess is less likely. :think
If it's on PC1 then what may be failing is the routing from their personal PC2 to the hosting PC1's address.