Summary
When using Safari 11 or 12 for a manual testing and you click on an element, you might encounter a pop-up that reads "This Safari window is remotely controlled by an automated test."
This is caused by the new SafariDriver on Safari 11 and 12, and was implemented as a security precaution. This can also be reproduced locally, and is not a Sauce-specific issue.
Workaround
The current workaround for this is to click Stop session, and you can continue your manual test as normal.