Do you have the newest version? You may have to remove the Mod and then Re-Download it. The Bug you describe is one that was fixed with the latest update.

I can confirm the bug.
When I equip an axe:
- In the Primary slot, the weapon simple un-equip after an attack;
- In Both Hands, the axe goes to the Secondary slot after an attack.

I just downloaded the mod for the first time about one hour ago or less.
Cheers! :)

Check the update. The issue with the melee items switching hands or being removed should now be resolved. It seems the bug was reappearing once the knives were gone and a melee weapon was used. The knives that make contact with the zombies should now also be recoverable.Thank you for pointing out the bug. If you happen to run into any further issues, please let me know so that I can fix it. Thanks for trying out the mod.