Search results show duplicate topics (and 1/2 don't work)

Hello,

I am using RoboHelp 2017 on Windows 10. I have a project that I have been working on for several months, although I am not that familiar with RoboHelp other than this.

I generate Microsoft HTML output and recently ran into an issue: for reasons I don't understand, whenever I search for a topic in the generated output, it lists many of the resulting topics twice. Clicking one of the topics out of the pair brings up the topic as expected. Clicking the other topic listed always brings up a "This page can't be displayed" message. Sometimes the first topic listed doesn't work, sometimes it's the second. Here's a screen capture that hopefully displays the problem clearly:

Please let me know if there are any more details I can provide. I am really not sure what happened.

Thanks very much.