Since it affected multiple devices, it sounds like a date issue. Something expired on or about June 18, 2020, and when your device checks the date against the expiration, it stops working. It could be a Java signing certificate, an SSL certificate, an SSL Certificate Authority, or even a date overflow. Those things probably wouldn't show up in testing. The only thing to do is wait. Or download the most recent firmware, reverse engineer it, check for overflow conditions, then recompile and resign the package with your own certificates, then hope that your certificates validate any future updates.
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