Displacement doesn't work except randomly and with crashing.
1. Random successs if viewport and rendering to image will use the displacment at all: I have attached screenshots where I have only switched from and to viewport rendering in between. Scene is the simplest possible with a plane with a texture.
(the 3 screenhots show this and additionally the view from the camera as rendered in viewport and as it looks when rendered to image)
2a. If using displacement on a plane and then alt-d copy that the settings are not copied. Choosing the duplicated object one can see that displacements have reverted to "level".
2b. If trying to render this simple scene in viewport or to image we get an "ERROR | check the log " message and a blank screen.
I have attached a file for case 2 where only the internal checker patterns is used to displace two planes.
Macbook pro 2017, amd pro 560 (no egpus attached or used)
macos mojave 10.14