Logs can not be referenced in "View Logs" of "Policy Manager".
However,the logs file exist in the following directories.
A large number of API Gateway nodes in the cluster were attached.
Most of them were invalid nodes.
API Gateway 9.4 (AMI Appliance: gateway-9.4.00-8872-ami-centos-x86_64)
The log was properly displayed after removing all invalid nodes.