Hi Mark,
That’s the place, also in R19
It should be there, I tried to find an answer, but that problem hasn’t shown up in R19. I can’t re-produce this here either.
In your Maxon Folder, there is a “corelibs” folder, can you check anything with the name substance there? If there is something missing, we have the source of the problem perhaps.
What version you are on?
This is certainly a case for the support, but restart or even better, if you can update (if you are on a previous version of R19, eventually that might bring back what your need.
https://www.maxon.net/en-us/support/how-can-we-help/
All the best