Internal links break when I insert a new slide (Captivate 12.3)

I have been working on a project for several days/weeks, currently 40 long scrolling slides with several activities, custom quizzes, videos etc. I have also set up an internal navigation/TOC, using Go to slide actions. Everything works fine, until I insert a new slide.

If I insert a new slide - regular slide or quiz slide - all internal links break. Meaning, the Go to slide links are still set up correctly, there is no red dot, but in Preview or published all these links don't go to their linked slide, but to the next slide. No matter what I do. Relinking doesn't do anything. Even if I take out the newly inserted slide, all links still go to the next slide. The only thing that helped so far, is making a new project and copying every single slide over, setting up each and every link again. Then it works again for a while. Until I insert a new slide.

This happened the third time in a row now, so it doesn't seem to be just a random bug.

Is this a known problem? Does anyone have a solution that doesn't include rebuilding everything?