After playing around with the ICMP filter on wireshark, I noticed that my machine is making ICMP requests to the router regularly, which consistently fails:
I noticed that the subsequent ICMP requests which fail are using UDP on port 53. Could someone please explain what I'm looking at?
These are no ICMP requests. Instead they are the reaction to something done by your router: based on the information you show your router (192.168.0.4) was sending a UDP packet with source port 53 to your machine (192.168.0.205) and there is no socket on your machine which is expecting this packet. That's why your machine sends an ICMP unreachable back which includes the details of the unexpected packet.
Given that port 53 is DNS this might be caused by your machine sending a DNS request (destination port 53) to the DNS server on your router but then closing the socket which have sent the request before the reply from the DNS server is received (maybe because it took too long).
