Same happening to me in iOS 13.
It worked briefly after updating to iOS 13.1 and then stopped working again.
I used sysdiagnose to retrieve swcutil_show.txt and it shows the next update time for the entry in my app to be: 0001-01-01 03:54:56 +0000
I was curious about this value, so I did some digging. It seems that this value is the equivalent of
NSDate.distantPast, that is, a placeholder that indicates that the AASA file has never been downloaded and should be downloaded at the next opportunity.
As to your big picture problem, it’s possible that you’re being affected by a bug that’s causing downloads to hang indefinitely. Can you try retesting this on the current iOS 13.2 beta seed?
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