I just installed Zynaptiq’s “Unfilter” (and for testing purposes their free “Subspace”, too). Scanning the common VST3-folder will stall NU10 (and NU8). It works as expected in NU5.5.6, though, which makes me assume that there is a problem with newer versions of Nuendo rather than with the seemingly more obvious culprits.
I am using the VST 3.6.5 version of UNFILTER on Nuendo 10.0.20 (Windows 10 Home - 64 bit) without any issues. I do recall having issues with UNFILTER on my old machine running Windows 7 and Nuendo 10. You might experiment on a Windows 10 machine if possible to see if that solves the issue.