Digging Plastic

[Kyle]

I have about 19-20 lighthouses that overlap, max amulet and robotic shovel, can't seem to get any plastic, am I just extremely unlucky or is it impossible to amass plastic via digging in the single island mode?

I've also used the liquid luck potion and I have gotten one single plastic, it's just never over one and I basically only get one after digging the island over and over again a few dozen times, haven't gotten a stack bigger than one from digging and so far I've only ever found two plastic via digging.