Hello, I still haven't fixed my middle snap issue for rectangles on Drifhsigh, they don't appear, to elongate them horizontally and vertically, without using the stretch function.
On the 2017 version, in the hook shortcuts at the bottom, you right-click on the e-snap and you have the snapping parameters (in your case midpoint to check).
I'm not sure because it's about the magnetization and not the attachment points.
By searching: in user preference, go to "entity selection" then "Egrips options" and check the 1st box i.e. "enable entity handles (Egrip)