Hi there

From the note, I understand EMR workspace still shows workspace is not attached to cluster. Please note this error "Error Starting Kernel Workspace is not attached to cluster. Click 'Ok' to continue." Occurs when cluster is not correct attached correctly or the cluster does not have all the required applications for it to be attached to workspace.

I hope the above information is helpful. References:

https://docs.aws.amazon.com/emr/latest/ManagementGuide/emr-studio-create-use-clusters.html

I had this issue too.. A cluster I was using for a while just stopped working and threw an error about connection error and the cluster is not connected to the workspace. the error repeated even when I detached and attached again. the solution of me was to clone the cluster and use a newer EMR version.