Line offset is not supported on ArcGIS Enterprise 11.1 and older versions. Vector Tile Layer symbology's corrupted in Portal for ArcGIS Map Viewer. When you publish a vector tile layer package containing offsets to the Portal, it is not displayed properly when you zoom out of the map in the map viewer. The map viewer classic which is powered by the JavaScript 3.x does not show offsets, and the map viewer which is powered by the JavaScript API 4.x shows corrupted symbology when you zoom out of the map. I tested it in the 10.8, 10.8.1, 11.0 and 11.1 versions. This behavior is not a bug, the Portal is not designed to support line-offset. Line offset is supported on Mapbox but it's not supported on the portal for ArcGIS map viewer.
This is a traffic data with the line-offset, you can find the corruption as marked in red. (Portal for ArcGIS New Map Viewer)