There is an unexpected behavior in EM2D right now when fitting a model to an image.
The error shows up when the pixel size is fairly high (~2Å/pix).

The error message from GSL library is:
gsl: simplex.c:430: ERROR: nmsimplex_contract_by_best failed
Default GSL error handler invoked.

So far, I have tracked the error up to the function in the source code -
ProjectionFinder::get_complete_registration()
but not sure why it happens - might be from how python handles warning from gsl c++ code but that's just conjecture - will update if I get further in the next few days.