There was an error in my troubleshooting. It looks like both EDLs (display timecode vs display frame number) look perfectly fine.
I’m not going insane, since I’ve used EDLs a number of other times in all kinds of applications.
I tried testing the one offending clip in a 23.976 and 24fps timeline, and even with a simple one clip EDL, Speed grade adds a 100.5% time stretch to the clip.
The problem was fixed, however when I set Speedgrade to interpret the EDL as 24fps and the footage as 23.976.
The footage originated from a RED Epic shot at 24fps with a timebase of 24fps…. I’ll have to check and see if there was a dropped frame issue or, if during the transcode process Redcine-X interpreted the timecode as 23.976… which would be a bug on their end.
A little more troubleshooting awaits.