Hello Jack,
If ISAMKP traffic is seen in both directions, then the .etl file is more useful than the Wireshark trace; all but the first packet in each direction is encrypted, so it is difficult to guess what is causing the problem given just a Wireshark trace. The .etl file contains more information about the processing of the received packets.
The command "pktmon etl2txt [...]" is one way of viewing the contents of the .etl file, although much of the content will still not be understandable.
I am always happy to look at trace data - you can either post a link to the data here (potentially also requiring an "grant access" request be sent) or mail the data to me at either the short address in my avatar or gary.nebbett at outlook.com.
The Wireshark trace would have been adequate for some scenarios (e.g. no response to first ISAKMP packet), but if several packets are being exchanged then more insight into the packet contents is needed.
Gary