Pre check elligable.
 

So the airline swears blind I am pre check approved but every time I am directed to the general line. Have I done something to anger the TSA or am I doing something wrong?

Is this the TSA screener checking your boarding pass who's directing you to general screening or an airport/airline employee directing you to the general security line?

The screener

Your PreCheck determination is based in part on your flight, other passengers on your flight, and your flying profile. Each flight gets a risk score that is derived from factors like this. Start with the last thing first, if you don't fly very much or you don't participate in Global Entry, then you may not get PreCheck all that often (maybe less than half the time, but that's just a guess). As to the other factors, none of us know the secret sauce. You may occasionally get PreCheck, you may have long runs where you get it a lot, and then have long dry spells. I have a long record of success on one airline and can't get it to work more than half the time on another, despite being a Global Entry member.

Best thing to do is decode your boarding pass when you check in. That way, at least you know how much time to allow for security at the airport.

That sounds to me like a procedural problem with one airline, in that your known traveler number isn't getting into the SFPD.

From my reading of various threads, it seems that two reasons people fail to get PreCheck are 1) The name in the secure flight info is not the same as the name on the reservation, and 2) there is international travel on their itinerary.

Please note that for #1, online account name or name with the airline is not the same as the secure flight name for many airlines. You need to go to the specific secure flight section of the airline's online account.