I use Simple Traffic as well, but I fly into larger airports and haven’t seen this. If you go to Aerosoft’s website you’ll see that others have asked the same question and are told exactly as you indicated, that their app simply changes the liveries of the aircraft that MSFS gives it.
I assume the moderators moved your post because of your mention of the 3rd party addon. If you want to indicate that MSAsobo could be responsible for this activity, perhaps you could deinstall Simple Traffic and go to your airport again and see if the problem persists. If it does, then create a bug report for the issue (or search to see if one already exists).