Another plumber show's when he's not out ripping customers off he chases cars and lick's himself places civilized people don't even touch in public.

Call Moen to explain your problem. Have the plumber's name and number handy,Moen rep might like a word with him.

The bottom of your sink may be wood, the wood got wet and rotted away. You may be able to use a mirror to inspect the area where your faucet is attached.

some faucets use gaskets, some require caulking.

It's a granite countertop directly on top of the cabinets. I have looked under it with a mirror and I don't see how to tighten it. I really think it needs something added to it to keep it tight. I guess I'll call Moen for suggestions and call a different plumber who is open to trying a different set up. Thank you

the problem could be that u do not have a rubber seal - which helps the metal tightening ring stick tightly to the underside of the granite- often during installation this piece is lost and this issue arises. - further the faucet tightening procedure requires a special tool called a plumbers kit - maybe that was not used to tighten it - (although that would be rare)

see photo below of rubber piece we are referring to - review parts diagram of faucet in question and order if needed.