Investigate worrying warning from emcee

[andreufont]

Once in a while, while running the emcee sampler, I get the following error:

[/global/homes/f/font/.conda/envs/cupix/lib/python3.11/site-packages/emcee/moves/red_blue.py:99](https://jupyter.nersc.gov/user/font/perlmutter-login-node-base/lab/tree/global/cfs/cdirs/desi/users/font/Codes/cupix/notebooks/analysis/global/homes/f/font/.conda/envs/cupix/lib/python3.11/site-packages/emcee/moves/red_blue.py#line=98): RuntimeWarning: invalid value encountered in scalar subtract
  lnpdiff = f + nlp - state.log_prob[j]

I'll try to add code to reproduce this