Have you completed any other mysteries in the area?
Im only missing Cordelia of the three Daughters of Lerion. I have completed several of the mysteries, both before and after the bug.
Have you left the zone before returning?
The issue first arrived for me after I returned to the game, after saving and going to bed. The day before the bug I was able to try fight Cordelia for probably 30 times. No issues. When I restarted the game and returned I could not interact.I tried to leave the zone, fast travel to other locations and return, reload the save, complete missions (both main and other), travel to Asgard/Jotunheimen and return. Did not work on the old patch, nor on Patch 1.04. Tried all of this on both patches.
Did you complete any other main quests before returning?
I have completed many main quest missions since I discovered the bug, but I had not done any missions (Main or other, including mysteries/wealth/etc.) between the time I was able to summon Cordelia and not. I'm, however, not 100% if I went to bed because I was not able to interact with the corpse or not, but I believe I was able to.
Have you been able to interact with the other 2 corpses for the Daughters of Lerion mysteries? Which daughters have you been able to successfully interact with?
Yes. I have completed both the two other Daughters of Lerion mysteries. Cordelia was the third one I attempted. I did them in a sequential order, so I did not jump between them without completing them.
I hope this will help you finding a solution to the bug. I really appreciate that you are working hard to solve this, however, I must be honest and say that I am a bit dissapointed that there has been so many bugs - especially the ones like this that is in my - opinion - gamebreaking. All in all, thank you for one of the best games in the series, love it, and hope I can wear Thor's armor soon.
Edit: In additon, I want to note that It seems like my experience have been somewhat different from many others; I did get to interact with Cordelia many times - not only 3 or 4 times - before the bug appeared.