Did you try the door anyway with all your characters? (unlikely the issue if you redid the fight multiple times, though)
Please email email@example.com, with a description of the problem and the report.zip file generated by the D:OS support tool
(for the PC version). The report will contain system and game information, any crash dumps, and your saved games. If file size is an issue, any saves not related to the problem can be deleted (so leave your latest save, and the most recent one before entering).