So, here is where I am with this buck converter.
Problem description: I'm seeing a switch-off lag between GS pins of the highside mosfet. Or in other words: the HS mosfet is not properly switching off.
Details: I'm using a FAN73932MX half bridge driver. The PWM signal is coming from my Rigol DG1022U @350 kHz, at 50% duty cycle. The mosfets are SIHB12N60E-GE3. Input capacitance is 120 uF on the PCB (input voltage is for the images below 38V), the inductor is 1mH, output capacitance 82uF, after the inductor I have a 100 kOhm resistor from output to ground and a big load resistor of about 220 Ohms.
Here is the datasheet application of the driver (as said, for the load I have a inductor, parallel capacitor and a resistor).

On my PCB, gate resistors are 10 Ohm in series and 22kOhm between GS.
The lag I'm talking about:

The yellow trace measures low-side GS signal and teal measures high-side GS signal. Vertical cursors show a dead time of ~400ns, which is factory provided by the driver. What is interesting with the lag is that it remains even when I remove everything from the output, remove the load from the circuit altogether or when I replace it with a purely resistive load. A very low impedance load lessens the lag (with the cost of several watts of heat), but does not remove it. As you see, there is no switch-off lag at the low-side GS.

The PCB layout is really quite minimalistic, there should not be any serious leakage inductance. As you see, the mosfets have large heatsinks in place for further higher dissipation experiments.

Here is the same waveform and same drive settings, but all load removed from the output. Purple trace is from the junction between HS and LS mosfet (Vs pin of driver).

Here there is a 150 Ohm resistor at the output.
Question: what's up wit the lag and how do I get rid of it? I've run a similar circuit at similar frequencies with the same driver and have seen no problems, with mosfets that have several times more capacitance (Coss, Cgs, Cds etc).