Polaris won't climb walls anymore.

[mphare]

What happened to my Polaris (280)?
A few weeks back I had to replace the Backup Valve as the original one had developed a crack.
I don't know if it started then, or before. I assumed it didn't climb walls before because a lot of the water power was diverted out the crack. But now, the crack is gone, the hose doesn't have any leaks and the thing still continues to get stuck in a corner and just sit there.

The Backup Valve eventually gets it out, but it always seems to find it's way back into the same corner. Everyday when I come home from work, it's in this same corner. It never used to be that way. It would always be in some random part of the pool.

I also notice I'm not getting the coverage I used to. Some parts of the pool look like they don't get any attention at all.. after weeks.

What should I look for a a root cause?