MAX2831 IQ output DC offset drifting

Hi!

For a research project I build a 2.4GHz receiving SDR front-end with a MAX2831. Because the chip is only used aas a receiver, the RXTX pin ist permanently pulled to ground. I set up all 16 registers according to the recommendended settings published in the chip manual. The chip is basically working but shows the effect that the DC offset ot the positive IQ outputs drift down from center voltage 1.1V to like 300-400mV and then now giving any output at all. The design is taken from MAX2831 EVM board. All VCC inputs are supplied by 2.85V which arestable. Ther Output is currently simply a 10kOhms resistor between N and P of each I qnd Q. I can change the DC bias my programming it over the SPI. That works to. But no matter if I go up to 1.45V or whatever: After about a minute I apply power, the output DC voltage drifts away. The both N output stay the same, voltage OK, signal OK.I also replaced it by another one, all the same.

Any ideas?