DRV8412: Parallel full bridge more only working in one direction

Part Number: DRV8412

I am using a DRV8412 in parallel full bridge mode 3, driving a peltier. I have followed the circuit in the Figure 17 of the datasheet. PWM is 200kHz. Peltier current 1.5Amax.

What I am seeing is that the bridge works fine in one direction using PWM_A (with PWM_B set to 0V), i.e. channels A/B switching nicely, and channels C/D driving low continuously to sink the return current.

But when I attempt to reverse the direction using PWM_B (with PWM_A set to 0V), I see channels C/D switching nicely, but channels A/B do not drive low, and so there is no current flow.

I have the same issue on multiple boards so not a soldering issue. All voltages check out ok, no faults reported either.

Any idea what might be explaining this?

Thanks,

Ian