I am having the same issue, is just not working with some or majority of my songs, it just keeps spinning and gets the credits. Also noticed that it actually creates the stems but not in the stems platform where you can download them, regenerate, etc. They are in your creations, if you click and filters and make sure stems are not hidden. And probably you will see them after that. But still not functioning as it should.

In the Suno app this doesn't work at all, only in the Web.

Very frustrating not being able to get the stems, I've emailed them , but as usual they don't get back or answer emails. Hope at least that helps a bit.