Based on my understanding, if client machine is mapping network drive then they cannot access file share via \FQDN. Is that right? Please feel free to let me know if I have any misunderstanding.
In order to get a more concreted idea of this issue, I would appreciate your help to collect the following information for further troubleshooting:
1.In order to narrow whether this issue is related with GPO mapping, please try to manually map network drive and then see if the problem still happens.
2.What's the OS version of your windows 10? 2004 or 20H2?
NSlookup FQDN result when the problem happens?
4.Check SMB client log on windows 10 to see if there are something related for us to troubleshooting.
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