No, that’s not the issue.
Nyquist plug-ins are just text files, so they work on both 32-bit and 64-bit Audacity.
Super 
Upgrading from 32-bit Audacity to 64-bit Audacity is not quite straightforward, and unfortunately it seems that plug-ins don’t always transfer across from one to the other as easily as one might hope.
My recommendation would be to make backup copies of your plug-ins (and any important “Macro” scripts that you might have created), and fully remove the 32-bit version of Audacity After uninstalling the 32-bit version, manually delete the hidden folder: "Users<username>\AppData\Roaming\audacity"
Also, if you installed FFmpeg for Audacity, uninstall that as well.
Then install the 64-bit version of Audacity, and check that it launches correctly.
Then, reinstall whatever plug-ins you want.
This approach is possibly more long-winded than really necessary, but hopefully it will ensure that the migration from 32-bit to 64-bit goes smoothly.
Note that if you use any VST effects, you will need 64-bit versions to use with 64-bit Audacity.