That’s a strange thing happening when editing tracks in V6. You have to do “Cleanup Tracks & Vias” to get rid of the warning.
[EDIT] Seemingly the PNS router produces track segments connected to a node on one end and dangling on the other. Since this happens congruent to the track you do not see that. If you are interested, hit ‘K’ to see the tracks “inner workings”.
This one bit me too. I can suggest turning off everything but Tracks and Vias in the Selection Filter in the lower right corner. Then run DRC and step through the errors and you will quickly find and be able to delete the “stubs”.