Detailing and Error "Line is slightly off axis..."

Revit is quite controlling about the tolerance we use to create things. This is because Revit's internal mathematics is ordered according the the scale or tolerance of buildings (inches/mms), not manufacturing tolerances (thousandths of inches/mms).

For example we cannot draw a line segment smaller than 1/32" (0.79mm). Revit will generate an error message, "Line is too short". Also, Revit will generate errors when we sketch a line at an angle that is as or more precise than 0.2 degress. This is the familiar warning Revit presents.

When you are doing large (fine) scale details that include and/or are representing manufactured parts/components it can be quite frustrating because the cad files we get from manufacturers include lines that are too short, in Revit's view, and are drawn at very precise angles. If you use these files and explode them (shouldn't routinely do that, explode them that is) in a project file you'll likely quickly acquire hundreds if not thousands of Reviewable Warnings (Tools menu > Review Warnings).

Too avoid inflicting this on your projects consider first using these cad files in a Detail Component family. Even if Revit generates these warnings in the family itself, when it is loaded into a project the warnings do not appear in the project's warning list. This will go a long way to cleaning up the list of Reviewable Warnings, rather reducing the list of warnings to review in the first place.

As for the details themselves, tiny fillets and short segments of linework is "lost" on Revit and in fact the short lines are deleted as "too short". Lines that are drawn at very precise angles can be left alone as they are not going to generate errors once loaded into the project. But consider that it may not be important to keep that degree of accuracy since your detail is not what the manufacturer will use to make the part, you are referring to/using their information after all.

Regarding exploding cad files in Revit, don't do it in projects and if you must do it in an isolated project file first, cleanup the line work and then paste or create components from the cleaned up linework. Exploding cad files proliferates object styles for each layer in the cad file. This will most likely unnecessarily bloat a project with objects styles, line patterns and linestyles, unless the details you use are extremely clean and well organized.