HTTPS proxy listener hanging, needs rebooting the box

We have two B2B servers 4.0.2/solaris2.6 in our DMZ acting as proxy for one B2B 4.0.2/solaris2.6 in a secured environment(reverse invoke). Every once in a while the HTTPS proxy listener on one of the DMZ boxes, accepting connections from outside/internet, get’s hung/deadlocked. And after this you cannot do anything with this B2B instance. You cannot kill the process, even as root, and we have to physically reboot the box to get rid of this zombie webMethods process and to be able start a fresh B2B instance. Both solaris boxes in DMZ have exact same configurations and patches installed. Nothing in logs also…
Any help would be much appreciated.