I have implemented an AD5412 into the carrier board of an industrial gas analyzer that I am designing. This assembly is in the BETA phase. Initial bench and environmental chamber tests were very favorable but after 3 months in our applications lab under long term testing we have had two failures. Both of these failures have had similar symptoms. The current output of the AD5412 will change from a range of 4ma - 20ma to 13ma - 50ma. I am using the boost transistor option with the recommended MJD31CG transistor. I have attached an image of my circuit. Any ideas on what could cause this would be greatly appreciated.