Hullo, team!
 
I just wanted to update this post to note that I figured this out. Apparently, for some reason I need a short Wait step before turning on the animation trigger for "attack".  At this point, I honestly can't remember if the attack animation was playing before the upgrade to 5.0 or not, but I am sure that if I don't have the Wait step before the Combatant Animation -> Play Attack step, the attack animation doesn't play.  This wait must also have at least some time (it's currently set to 0.1 sec), because if it's set to 0 seconds, the attack animation again does not play.
I'll update this thread if I learn anything more about this!
Cheers!
chainsaw