Well…I seem to have found the system tray icon again by starting Quick View from Programs>Western Digital>WD Smartware folder - but not sure why it disappeared in the first place.
Remains to be seen what happens with the recovery from sleep situation though.
Problem continues. Tried undoing “Enable auto…” via WD Security and then wanted to reinstate it but now that option is greyed out and I cannot re-enable it. Have raised a support ticket - will update when I know anything.
My issue was escalated to support (thanks Hamlet) and they responded. Solution was to disconnect MyPassport, uninstall WD Security, download latest version of WD Security from the download page and reinstall. Solved the problem. Enable auto now works. Thanks to support for quick help.