When I edit tracks via AIMP tag editor I add multiple genre tags with semicolon separator, like this: Indie Rock;Noise Rock;Neo-Psychedelia;Post-Punk Revival - four genres, Windows and AIMP guarantee it.
Poweramp v2 treated this kind of strings as intended - as multiple genres-substrings via semicolon separator. However, the newer app initially treats this genres as a single genre string, like that: Indie Rock;Noise Rock;Neo-Psychedelia;Post-Punk Revival - it's all the one genre, as Poweramp thinks
When I open Poweramp v3 tag editor and manually delete any random semicolon and add it again at the same place, the app finally treats that semicolon as substrings separator, i.e. deleting the last semicolon in the example string will turn one-genre-string into Indie Rock;Noise Rock;Neo-Psychedelia and Post-Punk Revival genres. ANOTHER EXAMPLE
AIMP multigenre separated string with different separators like Indie Rock/Noise Rock/Neo-Psychedelia;Post-Punk Revival turns into Poweramp single genre string Indie Rock/Noise Rock/Neo-Psychedelia/Post-Punk Revival (note the semicolon turned into backslash). Replace any backslash with the other backslash (like in the example above) - nothing realy gonna happen (unlike the example above). But replacing any backslash into semicolon finally splits that single string.