I was able to resolve the problem, but I'm not sure of the cause.
It looks like some empty objects got created and added to the timeline that weren?t tied to any bones or sprites. I think this caused the null value error in the instanceProto.findSprites function of the runtime.js where it is trying to get all of the ?timeline? elements out of the SCML around line 804.
I deleted these empty objects from within the Spriter UI and made sure they were also removed from the SCML and re-imported the SCML into Construct and it now runs fine now.
Here's one of these elements from the SCML...
<timeline id="21" name="object_000">
<key id="0" time="97" spin="0">
<object pivot_x="0" pivot_y="1"/>
</key>
<key id="1" time="196" spin="0">
<object pivot_x="0" pivot_y="1"/>
</key>
</timeline>