Any recommendations on how to easily fix this? It’s on the drivers side rear tire that the plastic piece is becoming disconnected. I’ve tried to reattach by just pushing the pins back into the holes but it keeps coming apart.

 

It looks like the snaps are damaged to me. Head to the dealer and buy a few new ones and swap them out.

 

They look like this, pull the broken ones out of the trim and push the new ones in. Then the trim will stay in place. Simple.

 

This just happened to a friend of mine's CX5 about 3 days ago. I pointed it out and it flew off on the highway before she got home. Today I noticed another CX5 with the piece missing. There's no way they don't know about this now.

 

It's not a defect, it's most often caused by hitting something or even someone kicking it.
Those type of plastic tabs are found everywhere and are easily broken.
I used to keep a stash on my boat as they held the windscreen to the console would occasionally snap off in rough water if I was going too fast.
In my area this happens on most all road vehicles that have these for fender flairs if they hit a snowbank and it doesn't take much of an impact.
An animal or bird strike or even a too vigorous hand washing of them can do it as well.
This type of plastic gets brittle with age.

 

Its cause by people running over curbs, traffic islands or parking blocks.
100% driver error.

I broke mine driving off-road.