A URL for your map would help so I could see it!
What you describe with some open and some closed sounds like a timing problem in which the map is still centering while they’re being opened.
Your POI that zooms to the wrong area: I don’t know, but check the individual map for it, perhaps the location saved for it doesn’t correspond to the title (for example you can title it “New York City” but put the marker in the middle of the ocean.
You asked about other ways to open POIs. You can also open them using javascript – for example after document ready. There’s a javascript example here:
http://mappresspro.com/mappress-documentation#toc-open-or-zoom-a-poi-using-javascript