RLC circuit: unexpected behaviour
I recommend inserting series elements - like 100R resistors - in the FET gate connections so you can monitor the gate waveforms. 

I suspect the FETs aren't turning off instantaneously and that during that time, the inductor current returns to one of the supply rails.

Also split the sense R into two, keep one where it is, put the other in series with the inductor, and monitor both currents. 

I think you'll see a positive spike in the inductor current that isn't in the capacitor current, while the slower of the FETs is still turning off. That's probably M2, returning current to the +ve rail.

If so, you can work on improving the gate drive waveforms.