Hello
Thank you for your question and reaching out. I can understand you are having issues related to adding users to Group from Domain A to Domain B,
The error message "A member could not be added to or removed from the local group because the member does not exist" is generic Windows error. When I search online, I found that this error could occurs when there is duplicate SID in computer OS. I found ntdsUtil tool to find and clean up duplicate SID.
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