Ok, think I get what's happening.
Some levels, like Bouncer, have the "Reset To Box" feature disabled.
This isn't a bug, but a big design flaw as it's not communicated in any way more than that the UI doesn't show the respawn hint.
This is something that should have been fixed for the final prototype build (latest build).
Not having Reset To Box should never make a level unplayable though.
Thank you for the feedback, I've added this to the design feature fix list!