The X10 messages are coming in the middle of the EZX10RF Group messages. An Insteon Group protocol consists of two Insteon messages. The first is a Group Broadcast message followed by a Group Cleanup message to each linked Responder, with the Responder (ISY PLM in this case) sending an ACK back to the EZX10RF for the Group Cleanup message. There is an X10 message occurring between the Group Broadcast and the Group Cleanup. That in and of itself is not an issue but the timing is such that the X10 message could easily get lost since it goes on the powerline in the blind (no ACK) and apparently without concern for anything else that is on the powerline at the time. In the detail trace there is a case where Group Cleanup was retried (two Group Cleanup messages) which suggests the timing between the EZX10RF writing the two Group messages and the alarm system putting out X10 messages are in conflict. Also the fact that the slight timing difference between the level 1 event trace and the level 3 event trace producing different results also suggests a timing issue between the Insteon messages being generated and the X10 message traffic.
Is there any way to create a delay in the X10 traffic coming from the alarm system so that they cannot overlap the Insteon message activity? Likely the alarm system is putting out multiple X10 messages to try and improve the reliability of X10, not anticipating the fact that the first X10 message would result in powerline traffic.
There is no means of changing the timing between the Group Broadcast and the Group Cleanup messages. The EZX10RF hands a Group On request to the internal PLM which then does all the processing to put the Insteon Group messages on the powerline and handle any needed retries. Insteon protocol is taking care of any issues that the overlapping X10 is causing Insteon but the alarm system has no way of knowing the X10 messages may be what is being lost.