Interesting. When I first got started with Unity I found really buggy behavior if you do any kind of physics calculations near world origin (0, 0, 0). It has a weird gravity well effect if you get too near it. I never found a satisfactory explanation for it but maybe this is it.
If you mean built-in Unity physics, then unlikely. All built-in physics stuff (either 3D physics which is PhysX, or 2D physics which is Box2D) are done entirely in C++ code and are unaffected by Mono float<->double shenanigans.