Parameter estimates not corresponding to chosen priors

• Operating System: Windows 10
• brms Version: 2.8

I am fitting a non-linear multilevel model using brms.
I chose my priors and fit the model.
However, the parameter estimate I get is very extreme,very unlikely to be drawn from the prior distribution I chose for this parameter. Also, the plot of the prior for this estimate looks different from the originally chosen prior.
Yet, when doing the pp_check, my model seems to be okay.

So I have two questions:

1. Why does this happen?

2. Is this something I should worry about? Does it mean the prior I chose is not a good one and I should revise my choice and find a better one?