Loo$psis_object is NULL despite saving psis

I am currently running some posterior predictive checks on a model I’ve fitted using brms+cmdstanr. For analyzing some of the ppc_loo and ppc_km outputs, I tried to create my psis object in order too retrieve the weights and psis values. However, when running the loo() function with the save_psis argument, the psis-object output remains NULL.

> loo_max <- loo(lognormal_max, save_psis = TRUE)
> loo_max$psis_object

All other outputs (estimates, pareto_k, n_eff, elpd_loo, looic etc) are displayed correctly, its only the psis_object that is not created. Is there anything obvious I am missing?

Other possibly useful infos:

  • fedora 35
  • brms version 2.16
  • loo version 2.4.1

Really scratching my head right now, looking forward to your answers.