One is when it attempts to generate vocals without a lyrics prompt. It's gibberish but just on the edge of comprehensibility. Sometimes it'll be entirely spoken word with no accompaniment. Very uncanny.
Another is transitioning between vocals and instrument in the same melody line. Like a humanesque voice holding a steady note at the end of a verse which seamlessly transitions into a saxophone sound and proceeds into a solo. Or vice versa, an instrumental morphing into a voice.
Finally is when the generation goes wrong and it starts spitting out absolute nonsensical sounds with no rhythm or melody, in a uniquely fragmented way I can't really describe. It feels like seeing the musical matrix, the inner thoughts of the AI.
Now I've written all that out and had a think about it, I'm tempted to sample these oddities and try to make something more structured out of them.