This happened to me yesterday and just about ruined my day.
Happened on my iMac running Mojave. It was very frustrating and seemed to come out of the blue. Ableton Live 10, and application I had just used, was suddenly not responding.
Saw that there was a newer version that I could install. Downloaded, installed, but on launching the first time it would hang at validation.
Did a first aid check on my internal SSD, fearing several sectors might have failed at once, scan was fine.
I checked console and found an anti-virus app I had installed trying to run to call home and then not being validated by the system, caught in a loop.
Launching other applications took forever and installing a new application (that would remove the one caught in a loop) wasnāt possible as it would also hang during the verification process on launch.
Eventually I manually removed all associated .plists and files, rebooted, and it was fine. But it took 2 hours.
Had no idea it was due to this, until someone at school posted it in our Slack this morning.