First of all, really cool Subtitle Player! Just noticed a few improvements to make the ssa parser a bit more resilient.
https://github.com/carsonip/Penguin-Subtitle-Player/blob/master/src/parsers/ssaparser.cpp

1.) New-Lines and White-Space Stripping
Each line should be able to strip (or skip) new-lines and white-spaces
2.) Not Hard-coding Character Removals
This runs the risk of assuming that word appeared on the expected line.
For example, lines like
formatLine = formatLine.remove(0, 8);
should really be detecting if the line starts with "Format:" after stripping white-spacing/new-lines as suggested above in 1.)

That being said, I just want to point out a few related issues that lead to either crashes or failures to read the dialogue lines.
(Note: "\n" represents a new line, and not literally those characters)

A.) Any leading/trailing white-space on the "[Events]" line will result in 00:00:00 timestamps as none of the dialogue lines will get read in.
B.) "[Events]\n" causes the program to crash.
This is because your parser expects the very next line after "[Events]" to contain the string "Format: "
C.) "\nDialogue: " Will cut-off any subsequent Dialogue lines