If you have a big round patch of dead grass then either the sump plug was loose or the lower oil seal was leaking.
The first is a dealer problem so Lowes owe you a new mower and the second is a factory problem so they owe you a new engine.
I am assuming that you are talking about a walk behind mower.
In this case put some more oil in it , put it up in the air and look for oil leaking out.
When a new mower comes in without oil the assumption is that the owner did not put any in.
However if you put it in and it all came out without causing your property to vanish in a pea soup fog then it had a chronic oil leak.
Usually oil leaking out from under the mower will coat the underside with a good layer of oil.
OTOH if you ran over a hose, wire or rope, these can damage the lower oil seal and the type of damage they do is obvious to the trained eye.
How much of a fuss you want to make of it is up to you.
But if the mower died on the 4th mow , and you have not abused it then it should be replaced.
Oil leaking under the mower will cause the grass clippings to bunch up and clog the discharge chute.
In a mulching mower it causes the grass to ball up and be deposited in big blobs.
Do you have any of the clogged up grass around ?
If so feel it for oilyness and take some of it with you when you take the mower back.
You can also go over Lowes head and register a complaint with the factory if it was a locally made mower.