"NLOPT_ROUNDOFF_LIMITED: Roundoff errors led to a breakdown of the
optimization algorithm. In this case, the returned minimum may still be
useful. (e.g. this error occurs in NEWUOA if one tries to achieve a
tolerance too close to machine precision.)"
I am not very familiar with this solver (so I may be doing something
wrong or misinterpreting something) but it looks like the scipy version
does not return a correct return code.