Launch of JalviewJS halting at "swingjs.api.Interface creating instance of sun.util.calendar.Gregorian"

Using the latest SwingJS (both SwingJS-site.zip and net.sf.j2s.core.jar -- version 3.2.4.09 [b]) the transpiler works fine (completes without error), but when launching JalviewJS halts at the output line

swingjs.api.Interface creating instance of sun.util.calendar.Gregorian

whilst the browser's Web Console has the following error:

[Firefox]
TypeError: g.html5Applet is undefined swingjs2.js line 16281 > eval:176:1
    <anonymous> swingjs/j2s/jalview/util/Platform.js:176
    <anonymous> swingjs/j2s/jalview/bin/Cache.js:257
    <anonymous> swingjs/j2s/jalview/bin/Cache.js:215
    <anonymous> swingjs/j2s/jalview/bin/Jalview.js:55
    <anonymous> swingjs/j2s/jalview/bin/Jalview.js:32
    <anonymous> swingjs/j2s/swingjs/JSDummyApplet.js:27

[Chrome]
Uncaught TypeError: Cannot read property '_uniqueId' of undefined
    at Function.eval [as getUniqueAppletID$] (swingjs/j2s/jalview/util/Platform.js:176)
    at Function.eval [as getProperty$S] (swingjs/j2s/jalview/bin/Cache.js:257)
    at Function.eval [as loadBuildProperties$Z] (swingjs/j2s/jalview/bin/Cache.js:215)
    at Object.eval [as doMain$SA] (swingjs/j2s/jalview/bin/Jalview.js:55)
    at eval (swingjs/j2s/jalview/bin/Jalview.js:32)
    at eval (swingjs/j2s/swingjs/JSDummyApplet.js:27)