Additional information.... IT guy found out if you go to Tools\Compatibility View in IE 11 and disable "Display intranet sites in Compatibility View" - search works fine on Sharepoint.
Our issue is... why did this work fine with our previous builds under RoboHelp 9 with IE 11, but it is broken now? Is it like the above referenced issue with HTML5 output where some script is out of whack?
It's not the same issue as the link relates to Responsive HTML5 help. The fix for that was in Update 2. Your post is about WebHelp with Sharepoint and that is a different animal.
WebHelp has no connection with HTML5 so anything in that forum has nothing to do with your problem.
If the solution you have found is not an acceptable one, you will need to log a bug report. Please follow this link to report bugs and request features. The more people who do so, the higher it gets prioritised.
Post the link to that bug in this thread and others can vote for it.
Hazarding a guess, maybe RoboHelp 9 generated the help in compatibility mode.
See www.grainge.org for RoboHelp and Authoring information