Following error is seen at the PATROL Agent(PA) startup:

Security policy is either missing or unreadable: /etc/patrol.d/security_policy_v3.0/proxy.plc/common /etc/patrol.d/security_policy_v3.0/proxy.plc/client /etc/patrol.d/security_policy_v3.0/proxy.plc/common /etc/patrol.d/security_policy_v3.0/proxy.plc/client

Extract from PA error log is as follows:

Thu Jun 16 08:30:25 2021: Enabling Integration Service support subsystem.
Thu Jun 16 08:30:25 2021: ESS Error: ESS_Policy_InitSecurityPolicy() failed >-4<
Thu Jun 16 08:30:25 2021: ESS Error: Security policy is either missing or unreadable: /etc/patrol.d/security_policy_v3.0/proxy.plc/common /etc/patrol.d/security_policy_v3.0/proxy.plc/client /etc/patrol.d/security_policy_v3.0/proxy.plc/common /etc/patrol.d/security_policy_v3.0/proxy.plc/client >-4<
Thu Jun 16 08:30:25 2021: Integration Service Client policy should be at security level 2. Current Level = -1.

These are the permissions in place:
/etc/patrol.d/security_policy_v3.0:
total 144
drwxr-xr-x 3 root sys 8192 Jun 15 11:14 .
drwxr-xr-x 4 root sys 8192 Jun 15 11:14 ..
-rw------- 1 root sys 866 Jun 15 11:14 agent.plc
drwxr-xr-x 2 root sys 96 Jun 15 11:14 bak
-rw-r--r-- 1 root sys 226 Jun 15 11:14 client.plc
-rw-r--r-- 1 root sys 549 Jun 15 11:14 esi.plc
-rw------- 1 root sys 1240 Jun 15 11:14 proxy.plc
-rw-r--r-- 1 root sys 40 Jun 15 11:14 signer.plc
-rw-r--r-- 1 root sys 1459 Jun 15 11:14 site.plc
-rw-r--r-- 1 root sys 46 Jun 15 11:14 verifier.plc

From the above listing, some of the policy(.plc) files have the correct permissions of 644 (-rw-r--r--), but agent.plc and proxy.plc only had 600 permissions (-rw-------).
This meant that the PATROL default account could not read these files.

These are the commands run as root during the install or post install using the .log_rootscripts file:

Firstly, for the .plc files with correct permissions:
/products/patrol/9.10.00/common/security/config_v3.0/policy_install.sh /products/patrol/9.10.00/common/security/config_v3.0/site_0.plc site.plc FALSE
/products/patrol/9.10.00/common/security/config_v3.0/policy_install.sh /products/patrol/9.10.00/common/security/config_v3.0/esi.plc esi.plc FALSE
/products/patrol/9.10.00/common/security/config_v3.0/policy_install.sh /products/patrol/9.10.00/common/security/config_v3.0/signer.plc signer.plc FALSE
/products/patrol/9.10.00/common/security/config_v3.0/policy_install.sh /products/patrol/9.10.00/common/security/config_v3.0/verifier.plc verifier.plc FALSE
/products/patrol/9.10.00/common/security/config_v3.0/policy_install.sh /products/patrol/9.10.00/common/security/config_v3.0/client.plc client.plc FALSE

The script policy_install.sh has the following line towards the end:
chmod 644 /etc/patrol.d/security_policy_v3.0/$dest_policy_file

This sets the correct permissions. Now let's look at problem files:
/bin/cp /products/patrol/9.10.00/Patrol3/security/agent.plc /etc/patrol.d/security_policy_v3.0/agent.plc
/bin/cp /products/patrol/9.10.00/Patrol3/security/proxy.plc /etc/patrol.d/security_policy_v3.0/proxy.plc

Per above, these files are simply copied with no chmod.
If by default, the root account does not create files with a umask of 022, then the permissions on these files will be wrong.
To resolve this, modify the permissions like this:

chmod 644 /etc/patrol.d/security_policy_v3.0/agent.plc
chmod 644 /etc/patrol.d/security_policy_v3.0/proxy.plc

Then restart the PA.
Please note that the PATROL installation assumes that the default umask will be 022. If it is not this, then files may be laid down with incorrect permissions in some cases.