[Martin Visser <martinvisser99@xxxxxxxxx>]

A couple of things.

I probably should have looked a lot more closely at your trace above. (Hint to all questioners - it is much more preferable if you can send a PCAP file rather than the text dump, it makes it easier to look at. But make sure your pcap doesn't have private data you don't wish to disclose)

The packets with SEQ 49235 and the accompanying ACK would indicate that the ACKs are not making it back to .15. It isn't clear what was happening closer to .15 - were any of the ping responses seen at all? If nothing was reaching the .15 box then you definitely did have a comms issues. 

Can you get trace close to .15 (or on that box).

You don't happen to have a duplicate IP address (check the ARP responses)?