I insert bookmark to a heading in a topic to link from a page to that heading. It happens in many topics that bookmarks are added automatically to every headings repeatedly. I had this problem since I started using Robohelp8 and it is continiued up to now with Robohelp17.
Here is a screenshot of repeated bookmarks. Any help is appreciated
This is not an issue I have ever been aware of.
Is the project on a local drive? Those versions do not work well on a network.
Are there any spaces in the bookmark when you create it.
Are the bookmarks in a-z characters?
Beyond that I have no ideas and unfortunately your version are out of Support.
My site www.grainge.org includes many free Authoring and RoboHelp resources that may be of help.