Insteon controllers send a Group message sequence to signal On and Off. The first message is a Group Broadcast which identifies the controller and the group number. There is no command retry associated with this message as it is not addressed to any specific responder. The second message in the Group sequence is a Group Cleanup Direct and this message is sent to each linked responder. This message has command retry associated with it as each responder must ACK the message. If the controller does not receive an ACK it resends the Group Cleanup Direct message.
The traced sequence is very strange because the Group Broadcast is being shown 5 times in a row, even though there is no command retry associated with that command. The Group Cleanup Direct, which does have command retry, is being sent only once and there is an ACK of that command from the PLM.
First let me make some assumptions which you should agree or disagree with. This is happening only with the EZX10RF. No other devices show multiple Group Broadcast messages being issued. The same sequence was observed from two different EZX10RF devices. If these assumptions are true then either two different EZX10RF devices have the same trait or there is some other variable involved. Is there more than one wireless X10 device producing the same results? What happens if you send the same X10 code directly over the powerline (no wireless)?
There are some issues with the ISY programming in that it produced 6 commands to the ApplianceLinc, one for each Group Broadcast and one for the Group Cleanup Direct. This is my assumption as I know nothing about how ISY works. If a command is being sent to the ApplianceLinc as a result of receiving a Group Broadcast (a normal Insteon device receiving the Group Broadcast would turn On/Off in response) the subsequent Group Cleanup Direct should have been ignored. Not a major issue and it has nothing to do with the multiple Group Broadcast messages.
One possibility is the RF signal is weak or intermittent, being sensed only long enough to generate the Group Broadcast but not long enough to trigger the Group Cleanup Direct. This seems like a low probability because it seems unlikely the command would be issued 5 times each time. The PLM could be repeating the Group Broadcast to the application (ISY in this case) but this also seems a low probability if the EZX10RF is the only device showing this sequence. If the same sequence is generated by multiple X10 wireless devices and it is not seen from any other Insteon device, that leaves the EZX10RF at the top of the list, except it is hard to believe multiple EZX10RF devices would fail the same way.
Perhaps more diagnosing will help. Trying different X10 wireless devices, sending the same X10 code from a wired X10 controller, making sure no other devices produce the same results.