To give you couple of concrete examples, the Continuumcoin has just been broken down in the above manner. It was functional just few weeks ago, but now none of the existing users can find each other anymore. Another even more interesting example is provided by the Unum; it has the same problem with synchronizing, plus the PoS part ceased functioning after a while in a way that prevent it from starting again even if the users could find each other again.
Are you sure that what is going on with Continuum is not
just forking? That can be fixed by deleting block database and
syncing with a good node. As for Unum, I took a look and it
seems ppl abandoned it long before the PoS stage started.
In any case, if PoS is nonfunctional it is likely to be a glitch
in the code (i.e. bad clone).
