I did some digging on this from an MEP parts perspective just recently but this was a problem identified with Revit 2020:
Release 2.16 was a major push to increase support for MEP components, but I haven’t a clear picture if there were restrictions on the older Revit APIs.
We have very limited instances where we branch our code by version, but we do target later versions for compatibility first.
If you can share a small sample file like the linked tread, we can take a closer look.