OK, confirmed. In fact init_nuts is never entered. I’m investigating if the fact that I initialize the step before calling sample could be the cause
step = pm.NUTS()
trace = pm.sample(draws=conf.block_size,
chains=1,
njobs=njobs,
discard_tuned_samples=conf.discard_tuned_sample,
tune=tune,
init ='advi+adapt_diag',#conf.init,
step=step)