I have the same problem and desperation, but with SQL Server. Lines randomly disappear in ArcGIS Pro (2.4 and 2.6) when zooming in / out. Recalculating or completely recreating spatial index does not fix it. In ArcMap all works well and as expected. I have imported these layers from PostgreSQL (outside of ESRI geodatabase) where I checked validity and simplicity, in other than ESRI software also all works great. I will try to use ESRI tools to check and repair geometry as AZendel recommended, as I guess that is the last thing I can do on my side. Update: As Esri presumes there can't be such thing as invalid geometry in Esri enterprise geodatabase, there are no tools to check / make sure. All tools on database level both in PostgreSQL and SQL server claim geometries are valid. Also as everything works great in ArcMap and non-Esri software, it must be ArcGIS Pro bug.
... View more