Bug happens whenever you instance a TerrainRegion and parent it to workspace in a Team Create enabled place.
EDIT: woops this bug has been reported multiple times already
Thank you for submitting this report. We are currently reviewing all bug reports to ensure we have not overlooked any ongoing issues. Since this issue was reported over two years ago, can you please confirm you are still experiencing the problem? If so, please respond to this thread, and we will investigate. If we do not receive any response within 30 days, we will consider this matter resolved. Thank you.