It is unclear why this might be happening, but simple science could explain why. The AirPods Max heavily feature the use of metal, such as the outer shell of the earcups. This means that when placed in different environments, like a place with high humidity, the heat and the cool metal will react with each other that will ultimately cause it to condense. Think of a glass of iced water placed in a warm room and you’ve got the idea.
https://twitter.com/klemanet/status/1344006938233810945
However, some users are claiming that they’ve never been in a humid environment, but it is possible that the heat could come from our bodies while we use the headphones, thus resulting in condensation. So far, we haven’t heard any reports of the AirPods Max not working after experiencing condensation, but it seems like it could be a potential issue, especially over an extended period of time.
Apple has yet to comment on the issue, but for a pair of $500 headphones, it would be quite an expensive fix.