I tried some time ago, but then I gave up , as far I remember there was a problem , something related to the ipsec sa ….. maybe ZS doesn’t clear the ipsec sa after the client disconnection , so if you want to reconnect , you need to restart the service , but maybe I’m wrong….you can try..here a good guide ..but …no way to work with asa ?? Could you tell a little more about the Zs config ? It looks strange , as I told I haven’t faced any issue to connect to asa from an host behind ZS..
greetings