What is the best way to fix an item that shows 1 as quantity on hand and quantity available in the Purchasing / Location section but doesn't show anything in the inventory detail section. Is there a way to adjust the inventory to 0?

I would first look at your bin put away worksheet.

OMG! How did I not think of that. You're awesome, Tim! Many thanks!

Trust me, I've been there! You're very welcome.

That is great advice and always where I start troubleshooting for this use case. If the Bin Putaway is empty than it most likely will be caused by someone turning the “Use Bins” Off & then On again on the Item record.