@dokken I installed dolfinx through conda and I am using version 0.4.1.
@nate It does seem to be related to that. I tried the following modification:
# interpolate f_data into the FEM basis
f_data_h = dolfinx.fem.Function(V)
f_data_h.interpolate(lambda x: np.ascontiguousarray(f_data(x[:2].T).T))
y_data_h = eval_func(f_data_h, x)
And the plots look correct now. Thanks for the help!