Edit: fixed relevant quote.
I’ve opened an issue here `CmdStanMCMC`'s function `stan_variable` does not handle arrays of vectors correctly. · Issue #361 · stan-dev/cmdstanpy · GitHub
I did run pip install --upgrade git+https://github.com/stan-dev/cmdstanpy before, so this should be up to date, shouldn’t it?
Edit: It gets weirder. This issue only arises if we take exactly one sample. I’ve updated the issue.