I used to sabotage all kinds of things: work, friends, personal relationships.
I can look back now and realize that it was because having a good healthy relationship (be it work or social) meant that I was doing something right.
It meant that I was doing something right.
That meant that my entire perception of myself (as being incompetent, no good, loser) was being challenged. Which, in turn, put me very very far out of my comfort zone.
Eventually I learned that I couldn't trust my own ability to judge myself or my actions. I learned to listen to what other people were saying, and tried to believe them.
From the sounds of things, you stay in the job until you start getting recognized for the good work you're doing, then that feeling of discomfort that comes from having "who you are" challenged creeps in, and you sabotage it to put you back into your comfort zone. Except your comfort zone isn't a healthy place to be.
I can trace my behaviors in this regard back to High School. It wasn't until I was about 27 that I started really getting a handle on it and realizing that I needed to not listen to myself, that I was taking my parents thoughts of me, carrying them with me, and inflicting them upon myself, and it was time to start listening to other people who told me what a good job I was doing, no matter how badly it made me squirm or how much I didn't believe them.
You have the ability to do good things. You are capable and reliable. Let that show through and tell those old voices in your head that this time you're not going to listen to them. Usually it's only the voices of the past, not the present, telling us we're failures. It's now time to listen to the voices in your present.