The only thing I've encountered with "lost" network shares is when Windows decides that my network is not the same private network and sets it to public. Once I identify the network as private from public, sharing is once again active and my network shares are restored. I've not had drive letters change on me. I don't have any MicroSD cards as Shares, just internal drives and a NAS. I suspect that your diagnosis is correct in that the issue is caused by them being MicroSD cards.
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