I thought I better seek help from others to make sure I'm not making a user error here before placing a bug report.
In using greyscale displacement maps (textures) in blender 2.80 I've noticed something seems to be going wrong with the way 2.80 reads the information in the image files.
As you can see image the comparisons below, 2.80 using the same 16bit tif displacement image results in what looks similar to bitdepth gradation banding lines/artefacts. 2.79 renders the displacement smoothly whereas 2.80 no matter what I do always has those ugly ridges/lines.
A bit about the setup:
1 plane, gloss shader (nothing plugged into it, roughness at 0)
displacement map from poliigon freebies "TilesRectangularMirrorGray001"
displacement map plugged straight into displacement output (note: also tried in blender 2.80 plugging disp map into 'displacement' node then into displacement output, no improvement) (note: tried both color and non-color options for image-file node, no help)
material set to "bump only" in 2.80 (note: also tried displacement+bump , displacement only in 2.80, including turning on experimental adaptive subivision, did not fix)
Note: 8bit 2.80 vs 2.79 appears similar in level of banding