Just for info, there’s a similar issue up on GitHub. It’s about the same exception, but it appears on runtime, not compile time - maybe there’s a connection there. I haven’t investigated it, though.
Did you properly add shader permutations in your .pdxfxlib?
Also, make sure platform level 10.1 is what is actually compiled (in your .pdxpkg).
Note that the system will be revamped to allow remote shader compilation of missing shaders and record those in an asset that can be reinjected in your project (that’s what we use recently internally, but will take some more polish before release, so probably in 1 or 2 months).