That does indeed sound like an sdcard permission issue. Strange bug, though. I’ve tested on S7 edge (stock Oreo), and S9+ (stock Q), and it’s working fine. This issue also has never been reported do far, and I believe that’s something people would’ve come across.
So it looks like an issue related to your device, or maybe to your particular chipset or OS version.
Can you tell us the specs of your tablet please? Maybe we can narrow it down somehow then. ?