When entering a PO and typing line items in manually, at the 3rd line, fields are not longer auto-populating

Manually enter line 1 - works, Manually enter line 2 - works, Manually enter line 3 - auto-population no longer works.

1st field not working: Description, then when fix description, then get a warehouse error "Item %s not found in Warehouse %s" This item is in the warehouse. And cannot move any further.

If I delete the manually entered 3rd line, I can add using pick lists and works fine.

When choose the exact same things from inventory, this works fine.

This just started recently in a stable system

Thanks

Terri