To reproduce this, run the following test with the standalone FX SDK (using an OpenJDK 10 build as a boot JDK).

$ gradle -PFULL_TEST=true :systemTests:test --tests test.sandbox.SandboxAppTest

The following two test cases will fail:

test.sandbox.SandboxAppTest > testJFXPanelApp FAILED
    junit.framework.AssertionFailedError: test.sandbox.app.JFXPanelApp: Application failed with a security exception
        at test.sandbox.SandboxAppTest.runSandboxedApp(SandboxAppTest.java:85)
        at test.sandbox.SandboxAppTest.runSandboxedApp(SandboxAppTest.java:51)
        at test.sandbox.SandboxAppTest.testJFXPanelApp(SandboxAppTest.java:114)

Here is the exception from the launched application:

java.security.AccessControlException: access denied ("java.lang.RuntimePermission" "accessClassInPackage.sun.java2d")
at java.base/java.security.AccessControlContext.checkPermission(AccessControlContext.java:472)
at java.base/java.security.AccessController.checkPermission(AccessController.java:895)
at java.base/java.lang.SecurityManager.checkPermission(SecurityManager.java:335)
at java.base/java.lang.SecurityManager.checkPackageAccess(SecurityManager.java:1311)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:186)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)
at javafx.swing/javafx.embed.swing.JFXPanel.updateComponentSize(JFXPanel.java:573)
at javafx.swing/javafx.embed.swing.JFXPanel.addNotify(JFXPanel.java:883)
at java.desktop/java.awt.Container.addNotify(Container.java:2797)
at java.desktop/javax.swing.JComponent.addNotify(JComponent.java:4783)
at java.desktop/java.awt.Container.addNotify(Container.java:2797)
at java.desktop/javax.swing.JComponent.addNotify(JComponent.java:4783)
at java.desktop/java.awt.Container.addNotify(Container.java:2797)
at java.desktop/javax.swing.JComponent.addNotify(JComponent.java:4783)
at java.desktop/javax.swing.JRootPane.addNotify(JRootPane.java:733)
at java.desktop/java.awt.Container.addNotify(Container.java:2797)
at java.desktop/java.awt.Window.addNotify(Window.java:786)
at java.desktop/java.awt.Frame.addNotify(Frame.java:490)
at java.desktop/java.awt.Window.pack(Window.java:824)
at test.sandbox.app.JFXPanelApp.initApp(JFXPanelApp.java:78)
at test.sandbox.app.JFXPanelApp.<init>(JFXPanelApp.java:136)
at test.sandbox.app.JFXPanelApp.lambda$runTest$3(JFXPanelApp.java:154)
at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:313)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
at java.desktop/java.awt.EventQueue.access$600(EventQueue.java:97)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(Native Method)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)


test.sandbox.SandboxAppTest > testJFXPanelImplicitExitApp FAILED
    junit.framework.AssertionFailedError: test.sandbox.app.JFXPanelImplicitExitApp: Application failed with a security exception
        at test.sandbox.SandboxAppTest.runSandboxedApp(SandboxAppTest.java:85)
        at test.sandbox.SandboxAppTest.testJFXPanelImplicitExitApp(SandboxAppTest.java:119)

The launched application for this test gets the same exception.