@leonardchrist I know I'm super late to the party, but the fact that the hub never ACKs the SYN ACK, plus the fact that it then re-xmits the SYN makes it seem like it never gets anything back. A couple obvious things to check would be the SN mask, and any possible ACLs/VLAN config on the switch ports. Alternatively, you could swap the PC/Hub switch ports and see if the behavior changes at all.

Alternatively, you could take a deeper look at the SYN ACK from the PC and compare it to the successful equivalent from the WiFi scenario. Hardware failure on the switchport, or hub, might cause it to fail MAC checksums.