Hi Michael,
Sorry for the inconvenience.
We checked with your reported query with the sample and attached video. We have considered “CheckAll method unchecks the previous checked nodes” as a bug in TreeView from our end. The fix for this issue will be included in Volume 2, 2021 release which is expected to be rolled out by the end of June 2021.
Please track the below feedback link to know the status of the issue.
We appreciate your patience.
Regards,
Sharon Sanchez S.