Duplicate Symbols on extended line.

[GIS_MLS]

Running Arcgis pro.  Have an existing line approx 80 meters in length and have a display layer with tick and auto measure labels at set intervals to produce a chainage display.  The existing line had make route function run over it to produce M values that then allow the chainage symbology to display correctly.  The issue I have is that I extended the line by adding some extra lines at the end of it and then merged preserving the exiting lines attributes.  Then when I do another make route command I get 2 chainage displays on the same merged line.  The original 80m chainage display and also the new full 200m display.  I’ve checked it’s only one line so how can I get the symbology to display only the new 200m chainage display.

[DuncanHornby]

Just thinking out aloud, when you extended the line have you mistakenly created a multi-part feature? Just go into edit mode and use the vertices tool and in the panel you'll see it list the vertices and if it has grouped them into parts that may be the source of your issue?

[GIS_MLS]

Yeah thanks

New at Arcgis Pro.

You put me on the right track.  The merged line was in 2 parts.  After trying a few things such as exploding and re snapping the vertices and checking if it had varying Z values (it had no Z values).  No luck with these options the string was merging into 2 parts.  Then I realised the original part had a numeric value in the M column and the new column had NaN value.  After a bit of research, I exploded the 2-part line and edited the M value of the original line via edit vertices and set it to NaN. I then remerged and it all merged into one part, and I was able to reroute it successfully so that there is only one change symbol.