I don't have the partner's logs. However, they did narrow it down to an issue with the blowfish cipher (that's what we were negotiating to). Knowing this, I changed the available method from the default (v. 6.0.7) of:
(i.e., I removed blowfish-cbc)
... and the issue went away. Maybe you could retest with only blowfish to see if there is an issue there?