Junos Pulse Crashing on El Capitan (10.11), Causing Keychain Issues?
I had the exact same issue. Basically, this happens only if you enable the checkbox "Save Settings" at the username/password prompt in Junos Pulse. If you do not enable this checkbox, it should not freeze at the next connection attempt.
Pulsesecure have released the software version 5.1R5.1 build 61437, where this issue has been fixed (I tested it today and it is working fine). I hope this helps.