I wouldn't worry if it's just the bumper cover that was cut. There are heat shields under the rear bumper area. I know from looking at the stealth hitch instructions it is only a minor trim of the one heat shield.HITCH UPDATE ...
I finally had a hitch installed, (there was a very long wait for the GLA hitch). Just as a side note, the hitch was installed to simply carry bikes.
I would like to start off by saying it just should not be this involved to install a hitch on what is supposed to be a SUV. As most of you know, part of the plastic bumper had to be cut away. If I had to do this again I simply would not. I would opt to spend twice as much to install a "stealth" type hitch so no cutting would be necessary. I am only staying this for any of you who are thinking about a hitch down the road for their GLA. However again, with the Stealth hitch you forfeit a lot of ground clearance. Thankfully you do not see any of the "cut" unless you crawl under the car.
The price was $350 installed as compared to a Stealth type hitch which was more than twice as much. I think the saddest part of the entire ordeal was we lost the hands free rear hatch release. I must have asked a dozen people if there would be any chance I would lose this ability and I was assured the sensors run across the entire rear of the vehicle and we would still be able to enjoy this option. Whatever the reason we no longer can extend our foot under the car to release the gate. I understand there are much worse things, however again, I paid for this option which is yet another option I can't use.
I did a lot of research before the installation and it was not until after install did someone tell me that "cutting part of the bumper" could cause some heat problems as this bumper deflects the heat. I have no idea how this small piece of missing plastic could deflect anything but it has me more than worried. I can only hope this is untrue, after all, a lot of GLA owners have had a hitch installed in this same manner.
As soon as I load the bikes I will take plenty of photos for any of those who are interested.
I would like to thank all the people who chimed in on this post as your time was greatly appreciated.
I'm in a holding pattern until my new GLA delivers, so hopefully by then steal hitches has a solution for the 2021 model.