I've been having the same issues on my new s9. I have a128gb memory card that had no issues at all in my s7. A few days after putting it into my s9 I've been getting a read write error. No data lost that I've noticed and I tend to get the error while web browsing rather than anything else. A reboot of the phone sorts it out for a while. Can leave the phone in my pocket all day with no issues, it's only when I'm actively using it. Uk based, 64gb S9 locked to vodafone.
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