Problem statement:  

If you have enabled security manager ( In Java 8 , security manager is enabled by default ) and using non-default external resources directory, then you might observe errors in the Job while loading external libraries. This is a known issue in the Platform August release. 

Example error: 

Provider com.mysql.cj.jdbc.Driver could not be instantiated

Affected Versions: August, 2023 Platform release

Solution: 

Add the external resource path to the security policy in the “Advanced Configuration” dialog of the deployment. 

Example: 

 For SDC, you should add below policy: 

grant codebase "file://${sdc.dist.dir}/externalResources/-" {

permission java.security.AllPermission;
}:

And for transformer, the equivalent is:

grant codebase "file://${transformer.dist.dir)/externalResources/-" {

    permission java.security.AllPermission;
};