Your problem is that the current limit transistor TIS98 has its collector going to a lower (more negative) voltage than the base and emitter. An NPN transistor requires the collector voltage to be more positive than the base and emitter voltage for proper operation.
To remedy this, add a resistor (Rnew) between the base of Q16 and the collector of the TIS98 control transistor. Its value should be calculated to supply the required current to fully turn on Q16 at maximum output current.
Then change the current limit transistor to a PNP and move it and the 0.5Ω shunt resistor to the emitter side of Q16.
Connect the shunt resistor in series with the emitter of Q16 and the +12V line.
Connect the collector of the current limit PNP to the base of Q16, the base of the current limit PNP to the junction of the 0.5Ω resistor and the emitter of Q16, and the emitter of the current limit PNP to the +12V line.
With that connection, when the current limit PNP starts to turn on from over-current, it will start adding current to the base-resistor junction at Q16. This will reduce the current available to turn on Q16, thus reducing its drive current and limiting the output.
Edit: Here's a schematic of the changes:
You likely will also have to add a compensation roll-off cap between the op amp (-) input and its output, since the added gain of the two control transistors may make the loop unstable and cause oscillations.