Chain freezes to one value

In the following figure, you see a bernoulli parameter which should select from two models. Parameters of the second model were shown by “c” and "sigma2. As you can see the Bernoulli parameter freezes to 1 and never goes to the second model. For second model I get only priors (C and sigma2). Bernoulli parameter also had a prior with a parameter “p” from a beta distribution (beta(1,1)). It seems that sampler works to find this, but the Bernoulli parameter always remain 1.

Is it an issue with the sampler?