Are you willing to test this with a few of the default workspaces? That is, change to a default workspace and see if the lag occurs. If it doesn't, then make a change to that workspace and see if the lag returns. If it doesn't, then you'll probably need to delete the old custom workspace and re-create it in the new version.
If changing a default workspace reintroduces the lag, then we need to look at your graphics and monitor setup.
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