for what it is worth, my guess is that you are doing your trigger movement to late, meaning you are on the move when the ball is delivered and this is then your head is getting outside the line of the ball, thus you miss the ball.
you could either ditch the trigger, stand still and keep your head still or trigger early and be still at the point the bowler is in his delivery stride.
It would also be likely that your trigger is moving you in front of middle, taking your eyes away from off stump and making you a big lbw candidate.
my suggestion is you film a net session and watch yourself bat...
buying a new bat is an unnecessary option... but one that as a forum member you are obliged to do ..!
i second to that, i had this feeling that i wasn't still when ball was delivered and it was confirmed by my batting partner at the other end, the reason i missed the length or was too late in shot, could be because of the swing in the air, i figured out i was kinda caught on the crease because i didn't play naturally on front foot, i was too busy trying to guess the swinging ball, it made me reluctant to come on front foot

i'm not gonna buy a new bat, i have few on my disposal, being said that, i prefer a medium-heavy bat but for this weekend i would try a lighter bat, just to see if it makes any difference in technique
i have recorded some footage playing against a bowling machine, i noticed 2 instances when i was LBW and both times my bat came a bit late alongwith very little foot movement, i can't imagine giving up trigger or backlift (i have been advised by quite a few good players) but whenever i have tried so in the nets, life was very hard for me specially a short-pitch ball, so i'll go to nets tonight and do some throw downs to get my mental inertia back, it's kinda getting on my nerves - LBW - i need my life back