This thread is still in my feed. And thanks for posting more details about it.
This is a fake Samsung?
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"KST" in the kernel string rather than "CST"* that's the first time I've seen that in a knock-off Samsung kernel string. Because that's one of the things I've often used to determine a real Samsung from a counterfeit.
But then there is still something rather funky going on with the internal storage on this phone.
* KST meaning Korea Standard Time, where Samsung usually builds their firmware. CST meaning China Standard Time, where Chinese knock-offs come from.