As for pm.save_trace, same error as the post above.
'NoneType' object is not iterable
There was a similar post in September.
Unable to load trace
arviz 0.5.1 seems to be the latest version.
The following codes are the things I tried just now.
Both resulted in slow very pm.traceplot.
1: Reinstall arviz via pip.
pip uninsall arviz
pip install git+https://github.com/arviz-devs/arviz
2: Reinstall arviz via conda
pip uninstall arviz
conda uninstall arviz
conda install -c conda-forge arviz