Mac OS Catalina 10.15.2 AMPDevicesAgent using 100% CPU
I still had this nagging problem on Big Sur, so it does not appear to be fixed (thoroughly). The iPhone entry in my Finder was permanently stuck at about one third and AMPDevicesAgent permanently took more than 99% of one CPU. Although the system remained responsive I noticed the fan blowing and more activity than I expected in the monitor.
I ended up force quitting AMPDevicesAgent in the activity monitor which removed the iPhone entry from my finder and the activity returned to normal. However I wanted my iPhone to be backed up so I also restarted the finder. This ended up in similarly high CPU usage as before, but AMPDevicesAgent never reached the levels it used to have. After a fairly long period of time (about 20 minutes) and several iPhone unlocks when it appeared to be stuck the process eventually settled down and finished the backup.
Now my iPhone is backed up and it appears in the finder with the usual information. AMPDevicesAgent is back at 0.1% where it is supposed to be. So all appears to be normal again and I keep my fingers crossed. I only found little info on the subject in the &quot;usual places&quot; like StackOverflow an Apple community forums.