To prevent a displacement texture “popping,” make sure the surface’s Use Min Screen attribute is turned off in the Secondary Tessellation Attributes section of its Attribute Editor. You can find the Use Min Screen attribute under the NURBS object shape node, in the Tessellation section, under Advanced Tessellation and under the Secondary Tessellation Attributes sub-section.

Use Min Screen tessellates a surface based on its distance from the camera and uses the screen space to determine how much tessellation is required (as opposed to object or world space). If the surface is moving toward or away from the camera and Use Min Screen is on, the tessellation changes over time, and the displaced texture pops.