I had this exact problem in REAPER with the initial versions of Ozone 8/Neutron 2. As one of my tests I tried to reproduce it in WaveLab but couldn’t. I am now using a beta of Ozone 8/Neutron 2 which will eventually be the next maintenance update and the problem is gone. I don’t know what the main cause was but there is maybe a chance it’s causing issues for you in WaveLab in a similar way it was causing problems for me in REAPER.
I would say there is a chance that iZotope plugins are causing a slow quit and it’s worth looking into further.