TCP 503 errors were intermittently occurring on the browsers.
Error went away once page is being refreshed.
TCP 503 Error
As it would be difficult to capture an intermittent issue, following steps below would help in capturing the issue in PCAP.
Note: you may add additional criteria to the above CPL to match only a certain traffic (Narrowing down the traffic is recommended as PCAP will be stopped if any user accidentally typed in a wrong address.
-This would stop PCAP if tcp_error is seen from the 10.30.147.76 IP address
client.address=10.30.147.76 exception.id=tcp_error diagnostic.stop(pcap)
-This would stop PCAP if tcp_error is seen coming from the 10.30.147.0/24 subnet
client.address=10.30.147.0/24 exception.id=tcp_error diagnostic.stop(pcap)