In the Quick View window, Serial or Lot Numbers are displaying twice, one quantity positive, one quantity negative.
This may happen, if you no longer use QuickBooks Enterprise Solutions Advanced Inventory with Multi Inventory Sites feature. You may have turned if off without transferring all items to one site as suggested and you sold an item.
Transfer all items to one site
If you sold an item before the transfer date, the item's may appear twice. Inventory and Lot/Serial Adjustments are not the same as transfers.
Before you disable the Multiple Inventory Sites feature:
When all inventory is transferred to one site, go back to Edit > Preferences and clear the checkbox for Multiple Inventory Sites is enabled.