Regarding Numpyro- sample get stuck in same value for all the rows

I am using python version 3.12 in my project.

Library: pymc

I am using Numpyro as a sampler for HBR model.

Why this sampler is providing flat posterior distribution within a chain for all the fixed effect parameters?

Previously it was working file but in my recent run the sampler value to much constant. After some times we get flat sample value. Why it happened? Any suggestions…..