Dear you are right , Amazon has come up with a new algorithm from April onwards This is called "Regional Discoverability " Not only you now many of us must be facing issues with the sales numbers after April because of it.
Now Your products will be shown only in the zone you belong to .i.e if you are Delhi Based your products will be shown only to people living in and around 300 km around you in North India.
This is the worst Amazon could do with small sellers or sellers with low margins .I already had a word with many higher level people in Amazon but they have no Solution to it. Many known sellers I know have cancelled their orders because of this new rule. Amazon has done this to make its loss making FC center business profitable . All this is done by arm twisting the small sellers.
HOW CAN YOU MAKE YOUR PRODUCT VISIBLE PAN INDIA AFTER THIS RULE : For that you need to put your stock in FC of other Zones . It is not so easy as it looks like.
For putting your stock in FC of other Zones you need to have a new GST numbers of other states. To have new GST numbers for other Zones, you need to have an Offices in those Zones/state . After you are done with it you need to add these FC centers to your GST as other place of business , Finally if all this is done you need to send your stock to these FC centers . Now your products will be visible across India.

Burden on sellers with this senseless rule:
Rental of the premises you hire for GST Numbers in other zone/zones.
Filling returns for all these GST numbers .
Extra capital to get extra stock for all these zones.
Transportation cost to send stock to these FC centers .
Extra loss in case of returnable product in every FC.
Extra Manpower to keep a track of all you orders in different Zones .

Hope this should clear you doubt and you would not make 10001th call to seller support.