Perhaps I've somehow recently introduced a bug or otherwise just never realised, but it appears that when I have the flight plan page open on the GNS530, it just about halves my FPS from 50 down to about 25.

 

Can someone else please test out for me if you also get lower FPS whilst on the flight plan page? Thank you.

Alright, figured out this had something to do with me editing the default GPS panel... although the specific XML files I've edited should not have been called by the aircraft. Not sure what happened but by disabling my edits to the default GPS has fixed the FPS issues with the Mindstar GNS530.