I was thinking about exactly this today while waiting to see if anyone replied to my question about this on another forum, which unfortunately no one has.
I don't think the quality of your ISP's connection has much bearing on this, a bad connection would show up in other ways and would be the same on wired as it is with wireless. As it apparently doesn't happen when you plug an ethernet cable in between your PC and router and use that instead of wireless this puts the problem down to between the wireless NIC in your PC and the wireless Access Point in your router.
If we take the strange MAC addresses in the packet capture as the PC's wireless NIC and the routers AP using MAC randomisation this puts the problem squarely on the router as the culprit of changing the the destination IP address. I suspect that due to the amount of wireless traffic coming from your PC (remember, each individual packet from your PC is being sent at least 4 times instead of just once) that it's somehow stuffing up the routing table in the router.
Anyway, your post seems to indicate that the problem is solved, so what did you do and is it still happening?
- Tim