Applet working with Java 8 update 162 and older doesn't work with update 171 and 172

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When using Java 8 update 162 and older, the applet loads and works as expected. When removing Java 8 update 162 and install Java 8 update 171 or 172, the applet errors with ClassNotFoundException. I don't see any reason for this in the 171 or 172 release notes or the 171 or 172 bug fixes. I'm using Windows 10 Pro version 1709 build 16299.371. The applet is signed with a certificate that is trusted and still valid. There aren't any exceptions in the Exception Site List and adding an exception for this site (it worked fine without one on Java 8u162) still displays the exception. Using Java 8 update 162 and older is still working on another PC.

When clearing the Application cache in the Java configuration, the applet's JAR file doesn't appear again in the cache.

Are you aware of any changes in Java 8u171 or 172 that affect applets? Do you have any suggestions to resolve this?