Yes, the supplied test subtitle file worked fine, subs moved with no crashing. On Windows, extracting the subtitle file from an mkv file, converting it to .ass with Subtitle Workshop, then using that .ass file has always worked fine. I then always do the same small tweak on the subtitle color and shadowing from my notes, without possessing comprehensive knowledge of all the formatting possibilities. That's the process that's always failed for me on Mac, even when the subtitle file has been extracted via Windows and verified to be working correctly on the Windows side. But after looking at your sample subtitle file that just worked on my mac, I conclude that it's user failure on my part: my lack of knowledge of the format and its headers must be a factor here. Here's how my file looks:
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,Rockwell Std,24,&H00FFFFFF,&H00FFFFFF,&H00000000,&H00C0C0C0,-1,0,0,0,100,100,0,0.00,0,3,0,2,20,20,20,1
Format: Marked, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:01:40.89,0:01:45.32,Default,Default,0000,0000,0000,,Four billion years ago, the first marine life formed.
I note that the top of your file is different, with moving subtitles and whatever. But I only ever need to embed simple subtitles, modifying those digits to for simple appearance tweaks. I tried overwriting the top of my file with the top of yours, plus adding the following style after your "john" style:
Style: Default,Rockwell Std,24,&H00FFFFFF,&H00FFFFFF,&H00000000,&H00C0C0C0,-1,0,0,0,100,100,0,0.00,0,3,0,2,20,20,20,1but that didn't work. So I assume I'm missing something simple about the file format that doesn't cause a problem on Windows, but does on macos. Can you tell me what I'm doing wrong?