BUG: `sample_smc` stalls on final stage

[tvwenger]

Describe the issue:

Sometimes, randomly as far as I can tell, sample_smc hangs when it reaches the final stage. This is a hard one to reproduce -- sometimes I can sample 100s of models before one hangs.

This has been discussed here: https://discourse.pymc.io/t/sample-smc-stalls-at-final-stage

@ricardoV94 suggested downgrading to 5.12.0 (before the new progress bars). This solves the issue -- I do not run into the hanging after 1000s of models sampled.

Reproduceable code example:

import pymc as pm
...
pm.sample_smc()

Error message:

PyMC version information:

5.27.0

Context for the issue:

No response