Question: What should I check when ACT isn't recording combat?
The first thing to check is to see if your game in question is actually writing to a log file. If ACT's title bar does not say "Log Active" in it, you may have the wrong log file opened or the game is not actually writing to that(or any) file.
Make sure that you have a parsing plugin enabled for your specific game and no other parsing plugins are enabled. Parsing plugins do not play well with each other. ACT will usually warn you on startup if it thinks you have absolutely no parsing plugins enabled, but it cannot detect if you have the wrong one.