Seems to me the sampler is rejecting all proposal. You should not call the step directly, instead do trace = pm.sample() which use the auto initialization with multiple chain.
Also, are you sure the input to B1 is valid?
Seems to me the sampler is rejecting all proposal. You should not call the step directly, instead do trace = pm.sample() which use the auto initialization with multiple chain.
Also, are you sure the input to B1 is valid?