You haven't included enough in your configs to troubleshoot this.
Your crypto ACL's probably don't match. Therefore it doesn't look like phase 2 is ever coming up. When you say that the "tunnel currently works fine..." are you showing encaps and decaps on both sides of the tunnel? I doubt you are. You could be because I've seen intermittent problems during phase 2 negotiation. Sometimes it'll work, sometimes it won't.
Also, I wouldn't doubt that there could be something wrong with your NAT's (or they could be just fine, no clue). Once your crypto acl's match, you need to take this back to the basics and think about a packet from source, through the phase 2 tunnel, to the destination, and what's happening and where it's happening. I can't follow your NAT's -- as I've never seen them written like that, and nowhere near enough information for me to try to understand it currently. Ensure your source and destination are what you would expect at each step of the transmission. '# sh log | inc' on the remote side will be your friend here.
I troubleshoot these half-blind at work all day pretty much with folks on the other end of the line. The only thing I have going for me in that case is that the local end, I can pretty much guarantee is correct before I even start the phone call.
