The Vaporeon Guest broke on me. It kept saying my relationship was at 15 with them (this was after I had hit this with every other guest), but I couldn't deepen the relationship by having sex or anything of the sort. This happened when I had Sam as a Vaporeon. On the reverse, Midna ended up having 15 relationship points with Sam and thus I got her instantly. And I had Sam as an Espeon when this happened.
Further more, as mentioned before, I've seen instances of choices being listed twice such as when talking to Gwen about Ditto after incurring their first transformation & seeing Ditto about progressing the plot further.
Sunny has an error message pop up. This does nothing; but it stops the relationship status message from showing up. Similar error messages happen at the entertainment; however nothing truly breaks in either case.
Finally, either it's not implemented yet, or the ability to switch into different forms overnight that have been deepened through the various mons don't work? The game breaks for me when trying to use that feature.