I may be missing something, but in my experiments Sequential play mode in the Animation COMP doesn’t seem to be working properly. Activating it doesn’t seem different in behavior from the “Locked to Timeline” play mode, and none of the Sequential specific controls have any effect.
“Use Input Index” did work with a Speed CHOP.
I compared this with the Animation COMP in my install of 077 (18900), and it worked fine there.