Index not loading in RH10 WebHelp output

We use RH10 (version 10.0.1.292) to generate WebHelp. Our current project has 3706 HTML topics and 13,119 index terms (MS-HKWD entries embedded in the HTML).

Recently, our users have encountered problems with their WebHelp index not loading properly: when the project is first opened, sometimes the index pane is empty. This is usually corrected by reloading the project, but it is frustrating for users and seems to be happening with greater frequency. The problem does not appear to be permanent and happens intermittently.

The majority of those reporting problems are running Windows 7 (service pack 1) and IE (versions 8, 9 or 10), although users have also reported problems using Mac OS and Firefox. (We have inserted the “meta tag fix” to emulate IE8.)

We wondered whether the problem could be something to do with the size of the index. Is there a maximum number of index keywords that can be contained in a RoboHTML10 project? Or a recommendation, if the maximum has not been defined?

I have looked for similar problems on the forum and Peter Grainge’s helpful site, but could only find an unanswered question from 2006.

We would appreciate any advice from the collective wisdom of the Robo community.