RH 11 Webhelp on MS Edge: TOC disappears after search

When our webhelp is viewed over the network on Windows 10 and Microsoft Edge, performing a search or clicking the Search button causes the TOC to disappear from the left pane until the pane is closed and reopened.

I have seen other threads on this issue for RH10, but I can't find a fix for RH11.

Does your WebHelp work well in Microsoft Edge?

I looks like there was a patch for this on RH10, and the second update for 2015 says it is fixed in there, but I'm having no luck finding a solution with RH11. We are on 11.0.4.291, which appears to be the latest.

https://blogs.adobe.com/techcomm/2015/11/robohelp-2015-release-update-2-released.html

http://www.wvanweelden.eu/articles/robohelp-patches-and-updates

Can anyone point me to a solution for RH11, or am I forced to upgrade to RH 2015?

Thanks in advance,

Judy