White goo from chicken ruins the dish
I suspect you're overcooking the chicken. This will happen with fish as well if you overcook it. The proteins are being pushed out of the meat along with water because they are shrinking too much. 

I cook chicken breast to about 150°F for three minutes (dark meat should be cooked to a higher temp in order to break down the sinew). When everyone tells you 165° that's because that's the temperature that kills most bacteria (to a 7 log10 reduction, or 1/10M). Cooking to 150° for three minutes does the same and the chicken is much moister, not stringy and dry. It's easy to test temperature in an oven but trickier in a pressure cooker. How are your vegetables coming out? Mushy and overcooked or just tender? 

If you cook sous vide you can cook at a lower temperature for much longer without negative effects. But I have found dark meat easier to get right with sous vide, and if I have the time I cook thighs and legs for eight hours at 158°F (but at least three or four).

Here's an article on temp and chicken that you may find helpful. I'd also suggest reading Kenji López-Alt's book. 

https://blog.thermoworks.com/chicken/thermal-tips-simple-roasted-chicken/