That exception seems to point to StaticWhiteList.parse line175 where the line that is being parsed is not recognized as a valid line. The first token on the parsed line is expected to be either "method" or "new" or "staticMethod" or "field" or "staticField" but the first token seems to be "SHA512:..."
I think that indicates that the scriptApproval.xml file in the Jenkins home directory has been damaged or contains incorrect content. After interactive testing of the two test jobs that I was using, my scriptApproval.xml file looks like this:
<?xml version='1.1' encoding='UTF-8'?>
<scriptApproval plugin="script-security@1365.v4778ca_84b_de5">
<approvedScriptHashes/>
<approvedSignatures>
<string>method groovy.json.JsonSlurperClassic parseText java.lang.String</string>
<string>new groovy.json.JsonSlurperClassic</string>
<string>staticMethod org.jenkinsci.plugins.scriptsecurity.scripts.ScriptApproval get</string>
</approvedSignatures>
<aclApprovedSignatures/>
<approvedClasspathEntries/>
<pendingScripts/>
<pendingSignatures/>
<pendingClasspathEntries/>
</scriptApproval>
However, I see in my own archived scriptApproval.xml file, I have lines that starts with "SHA152" as well, though they are in a configuration section called "approvedScriptHashes" and not in the section called "approvedSignatures".
Please provide an example script that shows the failure. Others are much more likely to investigate if there is an example script that shows the issue.