When (vector-valued) posterior distributions contain entries which are constrained (e.g. off-diagonal components of a diagonal matrix), and thus have no standard deviation, pm.traceplot can generate an ugly warning box that one or more of the variables wasn’t actually plotted:
We recently switched to arviz for plotting, which means it will now plot each dimension of every RV individually. Currently, you cannot plot everything today in one plot: https://github.com/arviz-devs/arviz/issues/94
KDE will fail if all the elements of the input array are nan or inf or exactly the same number, or very short array (less than 3 or so). trace_plot will fail for those case too, only variables before the failing point will be plotted. I will send a PR to better deal with these cases.