TLV431 precision voltage reference
Your stabilization issue could be one of temperature changes. Does it settle down after minutes?

You may also want to consider decreasing the value of the top burden resistor to increase current through the TLV431. 

Or you could be dumping too much current into the TLV431 such that it is self heating and causing a thermal shift of its characteristics. 

BTW, what is your input voltage and actual resistors that you selected?

Edit: So the supply is 5V with three 10K resistors. Some things to consider. With these resistors you have 3.3V-2.48V=0.82V across the top burden resistor. This results in 0.082mA for the load, shunt and reference divider. Seems way to low. 

You need to have the shunt current be ideally 10X the load current. You also want the current through the burden resistor to be ideally 10X the current through the reference divider. Try re-selecting the burden resistor to put 10mA through the shunt assuming that the load will be less than 1mA. A 100 ohm resistor may be a good starting point. 

Also putting more current in the shunt will more quickly stabilize its internal temperature.