I'm seeing the same thing on my end. At this point, it's related to Human Playback. If HP is turned of then expressions do not impact playback. When HP is turned on then it overrides expression playback settings. The result is that diddles (slashes) do not playback if HP is off.
Which expression are you using, the number in the upper left corner? I'll keep playing and see if I can find a solution other than turn HP off.
Mac OS 10.12, 10.14, 10.15, Win7, Win10
VDL2.5.5, Finale 2010-14.5, Finale 25-27
Kontakt 4-6, various other soft synths