disclaimer: I've never designed a current sense amplifier before
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When you pump in the 10uA current, what are the DC voltages Vdl and Vdlb? If they are both low, then probably your circuit it too big.
BTW, are the cross coupled PMOS devices a latch? If so, and if both Vdl and Vdlb are high, then maybe your latch just isn't strong enough.
Actually its a little tough to debug without some actual voltages in the circuit.
Aaron