I have experienced this issue before and it was related to a bad battery connection on the CGP board (the middle board in the IMC swing panel). However, it only affected the one car and not all the cars in the group. There must be some common communication problem within the group if it's happening to all the cars randomly. You can plug into the group and go to the Diagnostics screeen (F11) and choose Network Status to veiw communication status to the group and each individual car. I have seen poor communication if the system is not bonded well or if the communication line are not run in a separate conduit. Good Luck!
