The "find place" hang might be a different problem (which we can deal with later if necessary), but the "blank map squares" are probably covered in this thread
. Note that a simple "reinstall" is unlikely to help.
An excessively large number of overlay items is unlikely to be the problem, but you can export the whole overlay to a file, or only "Save Visible" (having used the "Hide"/"Visible" attributes). In principle you can also save any "category" or subcategory from the "tree" window (right-click on the item) but a bug (corrupt file created) has been reported when saving from the tree window.