The newest patch does NOT fix this issue. There is a BIG workaround for it though, that has allowed me to successfully complete the mission. Though it requires a bit of time and some fellow gaming friends.
You'll need a friend or sibling, whatever, who owns ME3 for the xbox. You'll also be needing a USB stick.
1. Go to this site and click "Register":
http://legion.cal24.pl/me2/ [It says "ME2, however, it works for ME3 as well.]
2. After you've registered and logged in, click "My Saves".
3. Click "Choose file" and navigate to your "Documents>Bioware>Mass Effect 3>Saves" and choose your .pcsav career. If you have more than one, it will be the one that was updated last. Click "Upload".
4. After it has uploaded, you will see the file followed by several buttons. Choose "Xbox export".
5. Navigate to where ever the file saved to. For most, it will be in your downloads folder as "SaveExport.xbsav".
6. Move this file to your USB stick.
7. Plug the USB stick into an xbox with Mass Effect 3 in it.
8. Load the career from your USB.
9. Go to Grissom and complete your mission. (Remember, you must do this BEFORE you finish Tuchanka's missions, or it will be gone!)
10. Save your game back to the USB stick.
11. Plug the USB back into your comp and navigate back to
http://legion.cal24.pl/me2/.
12. Login if necessary and head over to "My Saves" again. Click "Choose files" and navigate to your USB drive. Choose the .xbsav file and click "Upload" in your browser.
13. The file will appear beneath your previous upload (or whichever has the latest update time). Click "PC export".
14. Go back to your downloads folder (or where ever you saved the file) and copy the file.
15. Go back to "Downloads>Bioware>Mass Effect 3>Saves" and paste the file into it.
16. Open Mass Effect 3 and load the game (choose "Load" in the main menu, because sometimes it will load your old save instead, since the save did not originate within the PC game).
17. Your Grissom mission should now be complete! Hurray!
Please message me if you have any concerns or questions! Thanks!