If verifying files doesn't help, please email supportdos2@larian.com with a save where this can be reproduced (or a Dropbox or Google drive link, etc). If it happens in a new game/profile it is more likely system or install related, but if Qanna's vault was what got the lock working (rather than being random), it wouldn't hurt to check a save here.
If you are using any non-Larian mods, also include a list of those enabled and/or the modsettings.lsx file from your profile folder.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition\PlayerProfiles\<ProfileName>\Savegames\Story' folder.
In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder'.
