Fabia MK1 P0139 and P0170

Hello, I have a Skoda Fabia MK1 2002, 1.4MPI , and after a check engine light I scanned with VCDS, and show:

16523 - Oxygen (Lambda) Sensor B1S2

               P0139 - 35-10 - Response too Slow - Intermittent

16554 - Fuel Trim; Bank 1

              P0170 - 35-00 - Malfunction

I mention that I had the same errors about 1 year ago, and I changed both Lambda sensors (front and back), and the errors cleared. But now they come up again. Don't think the sensors are faulty after 1 year after replacement (that would be weird).  The car runs normal, start normal, everything fine, just this annoying error codes. 

Also I mention that a week ago I had an 'extra' error code, together with the ones above: 16825 - EVAP Emission Control Sys , P0441 - 35-10 - Incorrect flow - Intermitent, but when I scanned now, this error cleared, but the first 2 are still in place.

Any suggestions ?