Change from positive to negative and vice versa in the values of consecutive linterferograms

I have made a sequence of interferograms with a time frame of 12 days and with a spatial distance of less than 90 meters following the ESA manual.

I have sifted the result using only those pixels with coherence value > 0.4. I have taken linear displacement and terrain correction. I export the final file “displacement_TC” from SNAP to take it to R.

It is the temporary record of a very inclined slope where works have been carried out for a hydroelectric project. The civil works area covers an approximate area of 1.5 km. There, I have a population of pixels or points of 30,000 data per interferogram.

My surprise is to find that in several cases, the displacement values of one interferogram are all positive and in the immediately following one, all the values are negative. Since this is repeated several times in a sequence of 148 interferograms, I want to ask for help in understanding the problem. The questions are:

  1. Is there a problem with constructing an interferogram of a wide region, with large decorrelated areas, and selecting a subset where the coherence values are high (>0.7) and where the wrapped and unwrapped interferogram is of average quality?

  2. We have identified that the displacement values change from positive to negative and vice versa as “toad jump” (“salto de sapo” in spanish). What is the cause of this error? I find in a recent document that the negative values are changed to positive because the practical meaning of this does not make sense when talking about landslides on a very steep slope. However, it seems to me that it is a not very solid hypothesis in the study of interferometry.