Seems we're not the only ones.

I got around this by downloading the 2021 version here: https://www.kaggle.com/datasets/sssunyy/ade20k/data

And the 2016 version here: http://sceneparsing.csail.mit.edu/

Based on the conversation I found here, it looks like downloading from the official site gets you the 2021 version, but it's hard to know for sure without access.