Hello @Ed ,
1.Did you try the latest Version of Mac Remote Desktop 10.6.2 (1874)? Will it have the same issue?
https://install.appcenter.ms/orgs/rdmacios-k2vy/apps/microsoft-remote-desktop-for-mac/distribution_groups/all-users-of-microsoft-remote-desktop-for-mac
2.Please check if you saved domain accounts in the rdp file, and try to change password for problem account.
Best regards,
Leila
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