Safari is making me mad!
First killed the optional preference of ⌘+[0-9] of bookmark switching,
And now tab cycling is gone!
⌘ + [0-9] now seem to switch to the nth tab.
Tab cycling has always worked in El Cap for me using both of the original Safari 1.0 shortcuts:
⌘ + shift + [ or ] (prev/next) (i use this)
⌘ + shift + left arrow or right arrow (prev/next) (problem with this is it conflicts with text editing if box is active)