For all our valued clients we would like to inform you that when Esri released ArcGIS Pro 2.1 and ArcGIS 10.6, Esri upgraded the software compilers used to develop the software. Unfortunately this caused incompatibilities with ECW components previously used.
Esri has announced the ArcGIS (Desktop, Engine) 10.6 ECW Patch. This patch addresses support for the ECW raster format in ArcGIS 10.6 Desktop and Engine. It deals specifically with the issue of ECW display in ArcGIS. See https://support.esri.com/en/download/7583
ArcGIS Pro 2.1.2 Patch supports ECW files and is available from https://my.esri.com or via an automatic update in ArcGIS Pro