I have a problem very similar to this. I have Parallels 13.3 and am running Windows10 (latest build, all patches installed) within the VM with 8G memory assigned and 4 processors. My hardware is a macbook pro 2015 with 16G ram and the host OS is OSX 10.13.6
In the windows VM Task Monitor I sometimes see 100% CP usage. It is not clear what provokes this condition, but it certainly is not some errant windows app. When this condition occurs the windows VM becomes permanently sluggish. Although the CP usage does not remain always at 100%, it remains very high. Suspending windows from Parallels then takes a very long time (many minutes instead of a few tens of seconds). I so far have not been able reliably to replicate this problem, but it has occurred more than once and I have every expectation that it will continue to occur.
In the windows VM Task Monitor I sometimes see 100% CP usage. It is not clear what provokes this condition, but it certainly is not some errant windows app. When this condition occurs the windows VM becomes permanently sluggish. Although the CP usage does not remain always at 100%, it remains very high. Suspending windows from Parallels then takes a very long time (many minutes instead of a few tens of seconds). I so far have not been able reliably to replicate this problem, but it has occurred more than once and I have every expectation that it will continue to occur.