I wanted to see if anyone else is having the same experience. I just
upgraded my person Mac to 10.11 "El Capitan" and web interface (5.4) no
longer functions normally using Safari.
I have found a workaround that appears to work for this version of Safari.
1: Open Safari
2: From the FILE menu choose “New Private Window”
3: In the “Private” browser window enter web interface URL,
<http://mymobile.ssmhc.com> making sure the normal Safari window is not
attempting to render web interface (i.e. you entered the URL and left it
there) before opening the private browser window
4: Login normally and all functionality is as you would expect
Chrome and Firefox are unaffected by this issue.
Storefront is unaffected by this issue.