This problem occurs on some documents but not others.
I had success in fixing the problem (I have tried it on only one document) by changing Tools > Options > LibreOffice Writer > Comparison from "Auto" to "By word".
That may narrow the bug down a bit. I can supply an example privately and file another bug report if necessary, but will do so only if someone will take a look at it.
This problem occurs on some documents but not others.
I had success in fixing the problem (I have tried it on only one document) by changing Tools > Options > LibreOffice Writer > Comparison from "Auto" to "By word".
That may narrow the bug down a bit. I can supply an example privately and file another bug report if necessary, but will do so only if someone will take a look at it.