I just read through the instructions (we have the same monitor) and it says long periods of inactivity require longer warm-up times.
Do you leave the boat
for extended periods of time with the propane
breaker turned off? Try turning it on and letting it go through its cycle for a while and see what happens. Also, one thing I've noticed in the past is that the sensors don't like cold and humidity, such as in a poorly vented propane locker in the middle of winter.
We live aboard full time, so the propane breaker is always on except for when we leave the boat
for more than a day or two. Propane detectors don't detect propane if they're not turned on.