Combat is not being initiated properly as of the most recent patch (8.3.8).
This means more specifically that the buffs that should activate on initiation of combat, particularly from stealth, are not activating as they should. They are activating usually around 0.100 seconds after the combat initiating attack, when they should be (as they always have previously) activating before the damage of the initial attack is calculated.
All effects that I have tested that follow this formula (proc on initiation of combat by attack) uniformly do not work, so it is not p[roc effect specific, but rather the bug is with the initiation of combat itself.
As is visible here the combat is begun and the procs activated (in this case strike from the shadows and stygian, but this appears to apply to all other similar procs) AFTER the light attack from stealth that in theory should have initiated the combat.
As this appears to be a recent phenomenon (I noticed this on returning to play after a year or so of absence, when it was certainly not the case previously as my old CMX logs can confirm) and I can't find any changelogs that detail it, I'm going to presume this is a bug and not another stealth nerf to stealth gameplay.