PMOS cutoff not working well
That doesn't appear to be anything unusual.  From the datasheet you have a max of -1 uA @ Vds = -10 and Vgs =0.  If the Ids is at the max for the off state then what the switch is seeing is a 50 mV/1uA = about 50 KOhm load from your LDO's which will be highly non-linear as the voltage increases.  That seems about right.

You could decrease this leakage a bit further by driving the gate more positive but you can only do this slightly.  If you drive it too far positive the leakage will increase again because of GIDL (Gate Induced Drain Leakage).  Unfortunately the datasheet doesn't give these parameters.