Thank you for your post. I could believe there is what we call a "boundary condition" ("last" event conditions) that may not work. In my 40 years developing products, I am never surprised at the variety of boundary conditions we have seen and fixed.
You might try placing the lyrics again. I can believe the RW codes can get messed up if you do too much editing. That may solve your problem. I know I always do a BETTER on my 2nd, 3rd, 4th, etc. pass tapping the words to the music. I have found it takes me less time, and creates a better song highlighting more accurately, if I simply place the lyrics again instead of trying to edit. Just my two-cents.
I have documented your report to look at the next time we open the KHPro source code to make changes.