Hi there godcoder,
Thanks for joining us in Apple Support Communities! We understand you're asking how to prevent files from being locked when copied from your file sharing network to your Mac. We're glad you're here, and we can provide some guidance.
"Because passwords for some Windows users may be stored less securely, it’s a good idea to deselect the On checkbox next to each account when it’s not in use. Do this before you turn off file sharing on your Mac. Otherwise, the password is still active and stored in a less secure manner." Have a look at this link to learn more:
Set the protocol for file sharing on Mac
With that said, you can change your SMB encrypted connection options with the steps in the 'Set advanced file sharing options' section here:
Set up file sharing on Mac
Also, you may find the information in this link helpful:
Share Mac files with Windows users
Don't hesitate to follow up with us if we can be of any more help.
Take care.