I presume you have the slugs drilled the same as the other ball (s) ie span pitches etc.
If so, it could be a slight differance in the bevel which causes hang up.
Or the new slugs are rougher inside this a common cause when people have been using a ball for a long time the inside of the slug becomes polished with the thumb exiting, new slug may need working on or in.
Or worstly the new insert is moving on release...!!!!!!!
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Have no fear of perfection - you'll never reach it.....
Beer for the man, white wine fruit based drink for the lady.
Lane 1 for the man, storm fruit smelling ball for the lady.....
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