Hi,
It can stem from several reasons, but the more usual ones are:
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Too wide priors – did you try with more informative priors? Non-informative priors are usually a bad idea.
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Non-standardized predictors – I see you have a squared predictor; if it’s not standardized, the values can get huge and yield too complex of a geometry for the sampler.
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Missing values, zeros or out-of-domain data points somewhere.
You’ll find more information here.
Hope this helps 