RoboHelp 2019 Update 6 - Missing TOC link error
I've converted a project from RH 2019 Classic to RH 2019 Update 6 and found a possible bug where any topics in the TOC that point to a bookmark within a page show up as missing...

The properties appear okay:

If I re-add them using the New Page context menu, the red X appears and the links appears broken after a short while.

I can't open the page from the TOC, and I get red error messages saying that RH needs to be closed.
When I publish, the TOC does appear to work okay in a responsive layout.
The problem didn't exist in RH 2017 or 2019 Classic.
