When working on a Section type viewport in Civil 3D, the labels often disappear. Using the REGEN command makes them appear again. This may cause duplicate labels to be placed on a spot. The issue occurs in in Civil 3D 2023.2 and later releases but not in previous versions.
The AeccViewportOpt (System Variable) is set to ON.
As a performance enhancement feature, AeccViewportOpt system variable was introduced in Civil 3D 2023.2
When enabled the system variable controls the behavior of Section type viewports so that only objects that appear within the viewport range are generated and redrawn.
In previous versions, the entire drawing is redrawn even if only a portion of it was displayed in a Section viewport.
This system variable is enabled (set to On) by default.
Disable the AeccViewportOpt (System Variable)
Type the command AECCVIEWPORTOPT and set the value to OFF.
Read more about the AeccViewportOpt (System Variable).