I have Parallels 13 and I'm so far running High Sierra not Mojave. Luckly using apps like TG Pro you're able to set your own rules and maybe correct it. It appears to me that somehow parallels (or Windows inside the VM) make an abnormal use of CPU cores, setting just one of them to a very high usage (and thus rising the temperature on the specific used core to above the limit, while the average CPU temperature is still below it) causing OS fan rules not to spin accordingly to what would be expected. I then created rules on TG PRo to set all fans to full speed as soon as temperature starts to rise above acceptable. Found out that in most cases it was probably related to temperature (since some sensors were reading 100C close to the halting point). Since I noticed that the mac was getting really hot on every freeze (and just to be clear, this may not be the case with you since our problems appear to be slightly different - in my case the virtual machine AND the real machine got stuck with no way out), I installed TG Pro (an app to monitor temperature on all sensors). Far from a definitive solution, but try this:

2017 imac keeps freezing