Synchronous Buck High Side Driver - Why is the Fall Time of High-Side Gate Drive so Slow?
Comment from the OP: -


  The probes are connected between the gate and source of both MOSFETs
  directly.


Here's where you are likely screwing up. The ground connection on the probes are connected to each other to local ground on the oscilloscope so, in-effect, you are shorting out the lower MOSFET from drain to source.

If you want to do this properly use two probes that have their ground connection to 0V on the target circuit and probe the gate and the source of the top MOSFET. Look at the differential voltage by using the appropriate function on the o-scope.

Make sure both o-scope channels are set to DC.