First, upnp is disabled in the code itself, meaning clients can't connect to each other, only nodes - of which there currently only seems to be one that is active. I fixed that code and recompiled the wallet, but either that one node isn't relaying peers or nobody else is running the coin with a connection to that node.
Also a client and a node are the same thing. i guess the distinction you were making here is if one had port forwarding done or not though.
just run upgrade wallet= whatever the wallet version is to fix that. i already coded a fix for that without compromising the integrity of the feature structure of the wallet upgrade system. so upgrade=20500 would fix it. or if you have 0.2.4.9 then you run upgradewallet=20409. i made a post about this i think on the last page.
sounds like your colleagues wallet might have forked itself? unsure. would have to have debug logs to tell. although that is possible.
I've found all the issues I have encountered to be obvious from a coding perspective and the fixes trivial at best. I don't know anything about the state of the chain, or why the nodes have stopped relaying blocks. So take all this for what you will.
the three seed nodes are relaying blocks just fine. the explorer is actually disabled completely right now because they are upgrading wallet versions. one of them did crash for a little bit though
to address the, why can i not sync? issue. the best remedy is to try to rebootstrap and sync again. usually fixes the problem (or sync from scratch but wait a while)