I think this is SD card compatibility issue, I picked up a SanDisk 256 GB card and scanning seems to be working fine/not giving up -- generally things seem to be working as expected, though i'm waiting for a full scan to finish, however a quarter of my library seemed to scan and work okay.
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Finished a full scan, seems to have worked fine on the 250gb card, so seems fairly certain to be an SD compat issue
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Finished a full scan, seems to have worked fine on the 250gb card, so seems fairly certain to be an SD compat issue