Did you have a recent guest who may have reported you for something, not because it was true but because they weren’t nice guests? Some guests will report that there were bugs, or that something was “unsafe” or any one of a number of ridiculous things. Airbnb will even suspend a listing for “investigation” if a guest complains that there were cameras, without bothering to look at your listing first to see that yes, you do have have cameras and they are fully disclosed.
Airbnb considers hosts guilty until proven innocent. And that they refuse to tell you what you are being investigated for is truly Kafkaesque.