does it look like this (good quality)?
or does it look like this (bad quality)?
As mengdahl stated above: If the landslide was a non-coherent process, you cannot measure the displacement with DInSAR. Have a look at the coherence image over your landslide. If the values are low, decorrelation occured and you cannot reliably measure the displacement here.
Some reference on this:
#
source: https://core.ac.uk/download/pdf/43658687.pdf
Also here:
The interferometric SAR signal will decorrelate when the displacement gradient between adjacent pixels is higherthan half the wavelength during the selected time interval(Massonnet and Feigl, 1998).