Thought #1: broadheads always cause spine to react more weak so if the arrow spine is on the edge of too weak they will need the bow to be backed down in poundage. I would estimate that 28" 3-49's are on the edge of being weak with a 125 grain head for your rig (radical hard cam/high energy).

Thought #2: Shorter than spec. ATA usually means higher cable load which is higher poundage (and longer power stroke/draw length) so i'm betting that your poundage was more than you think for your spine estimate causing you to be even more over spined.

Thought #3: If you're going to get serious about doing your own tuning you've got to have a press and a scale so that you can keep cable tension, ATA and poundage in specified tolerance and matched to your arrow spine.