I did a search for this, and didn't see this specific issue.
I've been creating a series of misc alignments on each side of several alleys I'm designing. I create an existing ground profile to tie my corridor into. I tie it in both horizontally using the alignment and vertically using the profile. I physically create the profile off to the side so that I can see it. Just a quirk of mine that reassures me that things are ok.
I go through four blocks and everything creates and works fine. THEN, out of the blue, the profile doesn't work right. The alignment can be used as a target just fine, but the profile... even though physically created and visible (both profile view box and profile line)... does not show up under the profile tab in Prospector, and hence does not list as a possible target in the Corridor parameters.
I did not set or re-set anything that I am aware of. I tried deleting the alignments and profiles, saving, quitting, re-opening, and re-creating both the alignments and the profiles. Same result.
Now, get this: I did create a new alignment with the same polyline but a new temporary name. Then I created a profile. Worked fine. Go figure.
At this point I'm not seeking a solution because I did get it to work, but I am curious if anyone has heard of this and might know what happened and why.
Windows 10-64 Pro
8GB RAM (Home)
12GB RAM (Work)
AutoCAD Civil 3D 2019