I currently have Spotify on 2 devices, my main phone and an older iPhone I tend to use for running. I have reset my devices and am sure I only have those two in use. I've had an issue where by if I download my songs for offline use on a second device the first one resets to unavailable for offline. The songs I'm setting for offline are the ones I've added to my songs and there's about 2250ish, as I understand it I should be good for 3333 songs on each device up to a maximum of 3 devices.
I've had this issue for a while and have done without by avoiding downloading on both phones due to this issue and not wanting to be out and discovering the offline songs on my main device are no longer there. After trying this again with the same results it's now become rather annoying to the point I'm not getting what I should be and having to keep downloading my entire list is a nuisance and there's the unreliability of them not being there when I need them.