@evangeline - working on improving CmdStanPy error handling - issue is when subprocess throws error, try to get system message; make sure error code prints correctly · Issue #357 · stan-dev/cmdstanpy · GitHub
also, noticed that previously, error code -11 was reported and the solution was to rebuild CmdStan - C++ failure while compiling cmdstanpy model with reduce_sum_static - #11 by rok_cesnovar
it’s necessary to recompile CmdStan whenever there’s an software update to your C++ toolchain. this is because CmdStan pre-compiles as much of the world as it can beforehand (headers and libraries). when you recompile a Stan model, the system can’t link the newly compiled Stan model with the precompiled bits, resulting in some kind of system error.
whatever the cause of the error, more info would be useful so that we can robustify the code and add more troubleshooting info to the docs.