Steps to Reproduce
When constructing tiles, the dupe fell and/or hopped down via the fallen sand pillar (I didn't see the specifics). After they started choking, they kept switching between "moving to climb ladder" and "trying to climb up via the sand pile". The navigation view showed that both ways should have been navigable to reach the higher levels. The issue was resolved after BOTH sand tiles had been dug out. (with only one, the dupe still tried use it to get higher) I am unsure if this has to do with navigation or with a tiny cloud of oxygen drifting in and out of reach. Either way, it was quite inconvenient.
This issue has not been confirmed by a developer yet.