A Black Line in Terrain Correct Map

Fig 1: displacement map

Fig 2: subsequent Unwrapping phase map
Hello there,I practice DInSAR following the common procedure and produce a displacement map of my AOI. But as shown in Fig 1, it seems that something wrong happens. There exists a black line and pure blue area in the map.
Anyone kindly help me? Thanks in advance!

can you please zoom in and tell how many pixels it is wide?

The purple and blue areas at the edge are processing artefacts.
It also occurs in this tutorial and was removed using the subset operator: DEM generation with Sentinel-1 - Workflow and challenges

Thank you, sir. When I zoom in and zoom out to some extent, the black line funnily dispears. I take your advice and use the subset operator to deal with my filtered map. By the way, there are several lakes locating in my SLC image and I set coherence threshold to mask them, so are the wrapped phase of the lake areas still unwrapped in snaphu?

The only way to correctly mask out low coherence areas is described here: Is it the right way to create mask for phase unwrapping?

But it only works if the remaining areas are large enough and connected