kdenlive is a great video editor, running in kde (linux).
It has great features for subtitling but when you scissor a subtitle in two, it can overlap them. This can be fixed by exporting the srt file and then using, e.g., this go script [1]) and then import again.
If, like it was my case on a sorry occasion, you do not have access to the above script, you can try the following hack.