That means the Group Broadcast message that starts a Group command sequence, which all responders react to essentially simultaneously, is not being received by the responders. The PLM does not retry this message as it is not directed to any specific responder and therefore is not ACKed. The follow up Group Cleanup Direct message that is issued sequentially to each responder as part of a normal Group message sequence is for those rare cases where a responder did not see the Group Broadcast. If your responders are consistently not seeing/reacting to the Group Broadcast message it is an indication of powerline problems. Could be Access Points are not coupling the phases, the PLM signal is being attenuated by PC/UPS power supply, the EZSrve is plugged into a surge suppressing power strip which attenuates Insteon signals, noise, etc.