That inconsistent cut is a sign of a tough center layer portion in your plywood (if this is ply). You can use a bright light as an x-ray to see through and figure that stuff out both before (preventative) and after (forensically) your cut – provided your ply is thin enough.
Discussed here:
https://community.glowforge.com/t/trick-for-inspecting-plywood/15168?source_topic_id=17400
All may not be lost though, I find that if I get carefully aggressive with a box cutter I can complete the cut and salvage the piece.
I tend to cut through the top layer of the ply – intentionally too large --, snap the piece off at the cut, then sand the edge down. It’s saved me recutting several things.