I'm midway through HotU Chapter One and have retrieved the Djinni Bottle. When I summon Volkarion his dialogue window opens but he disappears before I can respond. I've retrieved the bottle multiple times and have tried summoning him in multiple places, but he always disappears very fast. If I pause, I'm able to get in one or two responses, but he still disappears long before getting to his store. I've submitted a bug report, but would greatly appreciate it if someone could post a workaround in the meantime. Thank you.
Edit: I don't know if there's an option to open stores using debug commands, but if there is I haven't been able to find out how. I was finally able to get Volkarion to open his store by spamming the hell out the pause button throughout his dialogue and then kept the game paused with his store open. Further attempts to summon him and shop with him result in him disappearing quickly, though, but the pause thing worked for me. I'm hoping that the problem doesn't persist in chapters two and three. I'll report back here if it does.