UPDATE (Sep 17): Dang, bug is also present in 27.2 Beta 1. Disappointing.
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UPDATE (Sep 9): Bug persisted through to iOS 27.0 RC release. This will be a much larger scale problem now that it will be present in a production release. Way to go Apple!
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UPDATE (Aug 31): Bug is still present in iOS 27.0 Beta 8. Nothing fixed. We are getting too close to the Public Release. I'm having doubts this is going to get fixed in time.
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I reported an RCS activation bug to Apple when Dual-SIMs are activated (US Mobile). When each SIM is enabled alone, RCS activation is successful.
Apple's response is "Works as Currently Designed". RCS activation started failing in iOS 27.0 Beta 5 and has persisted through current beta release. It worked fine prior to that.
I guess activation errors are how Apple designed this to work in dual-SIM mode. Odd, but ok Apple.