ArcGIS Pro: Polyline Symbology error: "Requested operation could not be completed"

[ElieRizk]

The issue persists in AGP 3..3.1 it is a show stopper to work with complex symbology for polyline layers. we are not able to move forward with such behavior. it is noted, the issue faced when using a feature class stored in file geodatabase and enterprise geodatabase.

we tried the steps mentioned in the following ESRI technical support page without success.https://support.esri.com/en-us/knowledge-base/error-requested-operation-could-not-be-completed-00002...

Also, someone mentioned that ESRI categorized this issue as a bug, but we aren't able to find the bug number.

"@ABishop kindly can you head up to the number of the bug mentioned in the URL you inserted in your message?

Here is a link to the BUG report site: https://support.esri.com/en/Search-Results#search?q=arcgis-pro&content-type=Bugs"

thank you,

ER,

[RTPL_AU]

I had this a few weeks ago. 
Could not figure it out and have not had time to lodge a bug; but did lodge a few Ideas.

All I can say is unless you specifically use 3.3 functionality just revert to 3.2/earlier.