Thanks for your comments and so sorry you ran into bugs!
I tried remapping place object to [SPACE] and was still able to place objects by positioning with the mouse and pressing [SPACE]. Is it possible you also mapped something else to [SPACE] after that? That could have caused [SPACE] to be removed as the input for place object. Which browser are you using? I’ll try to recreate the issue with it, in case it matters.
Unfortunately the items disappearing bug wasn’t discovered before the deadline. You can restart the level from the pause menu to workaround that issue, but it’s not ideal.