We have a strange issue with our ASA5520 acting as an easy VPN server. We want to run IPSEC over port 10000 just like we did on our VPN3000 concentrators. This works fine for like 5 days and then all of a sudden the ASA stops responding to IPSEC clients (both TCP and UDP) and drops all current IPSEC sessions. Not until I change the TCP port to something else, apply the running configuration and then change back to port 10000 again the ASA starts serving IPSEC clients again. It is like the VPN server functionality is completely turned off or something. There is no trace of any problems in the ASA logs.
Does anybody have any idea what could cause this problem?