I am also having this problem. The version I am using is Premiere Pro 13.0.3 (2019). I have tried several things like deleting the Media Cache via the Preferences window. I now have the app sending crash reports to Adobe. Today I had this issue 5 times in one afternoon. However, the program works great otherwise. I have no problems whatsever. Only when I Quit.
I have watched several YouTube videos about this problem and tried the solutions that are suggested. But they don't help.
I am surprised to see that this problem was already reported 17 months ago!
I ran into a hanging premiere on MBP'15 with macOS 10.12.6 and a discrete Radeon video. Every time i Quit Premiere even not opened any project, it became "Not responding" in Activity Monitor. I had to Force quit Premiere.
I tried everything I already knew and everything I could google during the day. At the end I found a solution myself:
1) open any project in premiere 2) call Premiere Console window by pushing CMD+F12 3) find and uncheck "GF.metal"
4) quit Premiere (yes, it hangs again so Force Quit it)
I'm having the same problem. When I close Premiere Pro everything closes but the app icon stays active and displays "Not Responding". I must then force close in order to reopen. The same thing happens about 90% of the time if I just close the project. I only have one project opened at a time.