This is likely below the controller’s Start Speed, so it will reduce the power to the layer’s Min setting. Depending on all those settings, the machine may be producing well under the power you expect.
A few years ago, I knocked the Start Speed down to 2 mm/s and watched a 60 W laser having trouble with various woods over maybe 6 mm:
Your veneered MDF may combine the worst of both worlds: an interior full of random chemicals and a textured exterior perfectly holding the soot. 