On linux, a possible cause is simply that the server is running out of memory and the OS decided to kill the service.
You can check this by running:
dmesg -T| grep -E -i -B100 'killed process'
You will see if the promonitor process has been killed because of out of memory problems
You can also check about available memory by running:
free -m
The memory truly available to application is stated below available in MB. Make sure there is at least enough memory for the monitoring process to start, according to its startup max memory (1 / 2 / 3 GB or more)
Resolution
The only way to solve this is to increase the memory of the host.