This is a known bug. I believe it's also mistakenly adding damage to the offhand hit (instead of +hit even without the feat that should do that.
Sound like 3 bugs.
1. Attacking with both main
and offhand with main attack without consuming a bonus action.
2. Adding my Str modifier to offhand weapon damage without Two Weapon Fighting.
3, The Bone club proccing heals on hits by other hands weapon.
