OK, under these circumstances, at first please measure the voltages with a load connected, e.g. 1k resistor in 1k range.
I assume, that U201, Q201, Q202 are fine, as the currents might work ok, as far as one can tell from your measurements.
If you have a 2nd 34401A, then you might measure the 80k resistor precisely, use it as a shunt, and measure 10µA and 500nA, using the 2nd DMM in its 1V and 100mV range, i.e. about 800mV @ 10µA and 40mV @ 500nA, but with much higher resolution. Simply use a calculator, and set the 34401A to R > 1010 Ohm. The absolute accuracy is not important, 1% is fine, but I just want to get rid of offsets and alike.
I assume that the transistor array might be damaged, or the 3rd FET which goes to GND.
Didn't we have that here, recently?
Sorry, need to sleep a bit now, continuation by tomorrow.
Frank