When you try to assign a CASE/LEAD object record using assignment rules, processes, or flows and the sharing on these objects is set to PRIVATE, the following message will be displayed depending on whether the user is in Classic or Lightning.
In Classic, the message is:
In Lightning, the messages displayed can be the following:
"Looks like there is a problem. You do not have the level of access necessary to perform the operation you requested. Please contact the owner of the record or your administrator if access is necessary"
or
"The requested resource does not exist."
This is working as designed. This is due to the fact that ownership of the record has been successfully transferred to the next owner and the current owner does not have the access to the record.
Note:
In Lightning Experience, the error message "The requested resource does not exist." may also occur when a user attempts to save a Lead that is being assigned to a Queue via assignment rules, but the user is not a member of that queue. While the lead is created successfully, the user loses access due to lack of queue membership.
To resolve this, ensure the user is added to the appropriate queue.
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