First note that you should not compare the results of running different versions of bench on different releases as bench may very well change from release to release. We mention that in the help for bench as well as at the bottom of the figure containing the numeric results of the bench run. [I don't know offhand if it did for release R2017b or not.] If you must compare two releases, run the older version of bench on both releases.
Even if the LU task did not change between release R2017a and R2017b the machine on which it was run appears to have changed. In R2017a the machine claiming the top spot in the table was listed as a Windows 7 machine; in R2017b it was listed as a Windows 10 machine.