Does anyone know an effective workaround if I want to sweep circles with small diameters along a path?
Try this sweep method: Dynamo Dictionary
If that doesn’t work, this might: Dynamo Dictionary
And if that still doesn’t work, what is your end goal after you make the solid? What is the unit on this 0.507 radius object? Feet? Meters?
Unfortunately, both alternatives do not work. they are effectively the small radius/diameter values.
I work in meters. From 0.025m down no sweep works anymore. I have also moved all objects to 0.0 to rule out a problem with the coordinates, unfortunately without any effect. i have attached a sample dyn and dwg.
I also noticed from this workflow that Dynamo has trouble picking points from 3D polylines.
The mangenta line is imported via the layer and the solids on the layer 0 should be the final result. But it always leaves out certain points (I have already noticed this in another project)…
Maybe you know a trick here too. 
testing sweep.dwg (1.6 MB)
testing sweep.dyn (286.9 KB)
This file is acting pretty weird on my system (locking up on open). Is this a standard DWG with only the polylines required to execute the dyn, or is it a full project?
This is an empty Civil3D drawing based on the Swiss CountryKit.
Here is the same again in an acadiso.dwt 
testing sweep-acadiso.dwg (481.6 KB)
Hmmm… still giving me fits, but I need to update C3D anyway (first by uninstalling and scrubbing the old version) so starting that shortly. Going to slow down getting you an answer though. Sorry in advance.
No Problem!
FYI i tested it with the version 2024 and 2025. I saved the .dyn file and the .dwt in V25!