The demographic breakdown in the YouGov/CBS poll looks suspect.
The % of Democratic pollees that are black is 62.5%. In 2008 when there was a black candidate running it was only 55%. The racial composition of the state hasn't changed since 2008 so why would a race feature two white candidates have a surge in black voters? if anything, one would expect the black vote to be less than 2008.
Even if the demographics were like the extraordinary 2008 primary, the 73% of black voters for Clinton would suggest a 6 point reduction in Clinton's lead. A 56/43 vote split. More likely the demographics are not so favorable as 2008, meaning an even closer race.