We are not aware of such cases in the past years and we will need reliable reproductions steps so that we can and reproduce the problem.
What you can do is to hide the Undo/Redo buttons from the toolbar of RadEditor, which will automatically disable the built-in Undo and Redo functionality of the control and enable the browser's one. This could help.
Other suggestion is to test with the latest R1 2019 SP1 version of the suite since it provides official support for all latest browser updates.
Make sure that the browser runs in native, but not in compatibility mode too.
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