I was able to see the submenus in gear up screen: armor, weapon etc, but after closing them then I was no longer able to open them. Then I entered another dungeon (with the base gear) and clicked an interactable (chest/barrel etc) and suddenly the armor and weapon menu's popped up and I could close them. The issue seems to be that they remained active, but invisible and could therefore not be opened again. After finishing the dungeon the gear up screen could open the armor and weapon menus again. Maybe I had closed the menu wrong by clicking outside of it, instead of the x button?
Also, using a healing potion on a killed party member revives them, but they are unable to act (but can soak up dmg) and they still die when leaving the dungeon.