you may not be shutting it off when you put it back in tool changer and the flashback sensor on the sheet metal may have been moved slightly.
there is a command to shut it off however if you never used it then the flashback reciever may be pointing up too high. the probe will shut off after a short time of being out of range of the reciever.
in the past doing a tool change put it out of range. it would shut off automatically.
watch the reciever lights and make sure they are not always on and recieving a probe signal. if it is the probe wont shut off unless you use the command.