Not sure what linux flavor you are running, but here are a couple of suggestions:
-Uninstall & then reinstall to see if that fixes issue
-Install DART, gather DART bundle, and parse logs to see why the vpnui is crashing after running; NOTE: vpnui = simply the AnyConnect user interface
-Verify that no 3rd party software is perhaps stopping AC from running
-If possible, I would recommend testing a newer AC client; 1: because 4.8.x is ancient/vulnerable, 2: could be an issue with versioning;
HTH!