I believe this is a result of a documentation "bug".
There are two different versions of the API which the New-NcVolClone cmdlet consumes, one at the cluster level and one at the SVM level. The SVM level API uses the two parameters you're specifying (JunctionActive and JunctionPath), however the cluster level API does not. When doing a cross-SVM volume clone the cluster level API must be used.
Here is how I believe the parameter sets for the two versions of the API should work...
The documentation for the New-NcVolClone cmdlet also includes two parameters, CachingPolicy and Option, which have no equivelant in the ONTAP 9.3 ZAPI docs. This could mean a few things, the most likely is that those options existed in earlier versions of ZAPI and are still there for legacy reasons, but could also be some "magic" happening in the cmdlet to apply additional options to the volume after it's cloned for convenience. It could also simply be a(nother) documentation bug.
I'm going to create a bug for this issue. If you are willing to PM me your mailing address, I'm happy to send you some stickers as a "bug bounty" : )
Hope that helps.
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