Your weight loss could have changed several possible factors in your bowling game:
finger sizes, span, pitch requirements, timing, release point, PAP, tilt, etc.
Your leaving the back row hints at your release being very different.
I'd also suspect timing changes (60 lbs is a LOT for any height person).
Any or all of these could mean your balls are no longer drilled correctly for spna pitches AND pin/CG/MB placements.
BTW congrats on the weight loss. I suspect your whole life has gotten better, or at least changed dramatically!! Hopefully, for the better. (Need a whole new wardrobe, expensive.)
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Just like hand grenades and horse shoes, in bowling you only have to get close ...