I know PBS has logs in many locations, but I keep forgetting which log has info. on why a node is down.
Please check the server logs, when the node goes does ( status = down)
source /etc/pbs.conf check $PBS_HOME/server_logs/YYYYMMDD
Sample server log :
12/16/2020 21:50:28;0002;Server@openpbs;Node;node01.openpbs.org;node down: communication closed