I submitted a version of this question 3 years ago. There has not been an answer. 662 developers are watching that question. As requested by KMT I submitted a bug report. Others had submitted a similar bug report before me.
As far as I can tell, nothing has been done to address this issue.
Not addressing this issue amounts to disturbing negligence. This is important!
WebView is flakey. It needs to be replaced.
Apple Engineering: Please accept responsibility for this issue and respond with a date when we can expect a solution.