H2O,

Your alkalinity is high but not crazy high and your CH is in the acceptable range (at least according to most of those "recommended levels" tables you see). I wouldn't worry about either for now.

Something is still eating your chlorine and really, no matter what it is, the cheapest and most effective recipe for fixing it is probably more chlorine. Dose up the chlorine to shock level as you're doing (10 or 15 ppm will probably work with your low CYA level), test frequently (like 3 times a day if you can), and keep adding chlorine as needed to bring it back up to your shock level. Once it holds free chlorine overnight you should be on the downhill side of this.

Good luck.