Hi,
Not the first time it happens, so this is repeatable. I launched Logic on a Mac with High Sierra. Then opened a project containing several Synchron Player instruments. Logic took some time, then the usual eLicenser missing message appeared.
I disconnected the eLicenser, connected it again, the clicked Retry in the message. Logic was no longer responding.
I tried to quit it. Then force quit it, but it couldn't be closed even this way.
I then tried to restart the Mac. No way: Logic, frozed, prevented shutdown.
I had to use the hardware power button to turn the Mac off and on.
If there is some log I can send you to see if you can understand what happened, I'll do.
Paolo