Thanks for the reply!
I did think it was something to do with the compiler, I have tried several ways to install them using the bash script in the past and the above is just my latest attempt.
Using ‘FAST_COMPILE’ (I had read about this but didn’t try it for some reason) PYMC3 does actually sample fine now but pretty slow, which is expected:
I’ll try via conda-forge and see if that changes anything and will also look into seeing if I can install / point to the compilers any better. At least this works now, thanks!