I had a similar bug, but I thought it was an intentional design because it allowed me to go underneath what I realized later was the level itself, and after some trial and error made it into the lower room connecting the tower and the series of ramps with the "Nothing for me here" painting. It was only later I realized that wasn't in the design haha. Completely backing out back to the lobby and reloading into the dream/echo fixed the issue for me.