[Plugin: WP Super Cache] preload not running on schedule

I’m working on a couple of strange issues with the preload cache feature in WP Super Cache. I’ve tried the development version, but the results seem to be the same either way.
First, The timer does not seem to be working. If I set it to be a 30m interval (for this troubleshooting) It will usually run the first, and sometimes a second time, but not beyond that. When I look in the cron tasks, I can see the scheduled event for the preload, but it is listed as a ‘one time’ job. Then it does not create another one time job subsequently.
The other issue I seem to be having is that the preloaded cache files seem to disappear in between. I have disabled garbage collection but the files drop out of the cache anyway. In the message about GC on the options page it clearly states that

“In ’Preload Mode’ regular garbage collection will only clean out old legacy files for known users, not the preloaded supercache files. “

I am happy to provide any other information that may be helpful.