Clean it up with mixture of a few spoon chlorine bleach and about a quart of warm water, use the same on the back of the flooring is you got there also. Run a fan for a few days allowing to dry and reinstall the flooring. Or you can call SERVEPRO and have them do mold remediation and go through your insurance (they will do a much better job)

Good luck

Where's the vapour barrier???? The 6mil clear plastic sheeting that should be under your vinyl?

They didnt install with a vapor barrier.

The LVT is waterprooof and has a underlayment attached. Install guide said do not install any underlayment (including 6mil poly)

From what I read it could void the lifetime warrenty as well.

Do you have any insight on my question of if those pictures looks like the beginning of mildew or mold?

I'm probably going to spend the $40 and send a sample to the lab, but looking for other's opinions on the visuals I uploaded.

Chris,

Put a few drops of household bleach on the dark spots, if the spots turn white or lighter color most likely this is mold or mildew and if they remain dark most likely this is dirt.