To replicate, follow these exact steps( I tried it with gnome-maps and demos/launcher on Fedora):

(1) Press and hold the left mouse button on the map view

(2) While doing (1), press and hold right mouse button

(3) While doing (1) and (2), move mouse

(4) Enjoy freeze

From what I managed to debug, the freeze is caused by an infinite loop in
champlain-view.c: view_find_suitable_zoom

Apparently, the sequence of events described above is recognized as a ClutterZoomGesture. 
The "zoom" signal (https://developer.gnome.org/clutter/stable/ClutterZoomAction.html#ClutterZoomAction-zoom ) is picked up by the view, and the callback ends up calling view_find_suitable_zoom() with factor == inf (this causes the infinite loop)

This looks like a clutter bug to me, but I cannot find any info on it. What do you think?

Regardless, I've made a fix/workaround patch for it: it adds a safety check to the while condition. In my opinion this check should be there even if this proves to be a clutter bug.

Another fix would be to discard the event or treat it differently.