Lookup filter Question -- Tricky One (Lightning)

Hey All Experts,
Its a tricky situation fail to get it. i am a newbie in SF. Here is the scenario --
There is a lookup filter on Product Interest field &
Product Brand is a PickList
what's happening is that out of 6 picklist values for Product Brands only one is causing Lookup functionality to fail i.e Products corresponding to that particular brand do'not show up in Product Interest field.
-Show All does nothing,
-Typing related values (from Workbench) does nothing,
-Adding a new product does not register new product with that particular brand.
-tried comparing WorkBench data with other brands no conclusion still
Any clues y'all might be able to provide. Thank you so much in advance.
Regards,
Sunny