WARNING [main] org.apache.tomcat.util.digester.SetPropertiesRule.begin Match [Server/Service/Connector] failed to set property [packetSize] to 
I see this warning when migrating from Tomcat 8 to 9 on JDK 8. The warning went away when packetSize="65536" property removed.
Apparently this property only applies to the AJP Connector. This is not a parameter that you should be overriding unless you are working deeply within the internals of AJP. So I recommend that you simply remove it.
Some people, when well-known sources tell them that fire will burn them, don't put their hands in the fire.
Some people, being skeptical, will put their hands in the fire, get burned, and learn not to put their hands in the fire.
And some people, believing that they know better than well-known sources, will claim it's a lie, put their hands in the fire, and continue to scream it's a lie even as their hands burn down to charred stumps.