Spotify Connect won't find my iPhone but other devices work fine

[Hollomau5]

About a week ago, Spotify stopped being able to find either of my two iPhones on Spotify Connect, but it can still find my tablet and PS4. I have tried logging in and out of Spotify on all devices several times.

This is annoying as when I'm working at my laptop with Spotify on, I like to be able to continue listening from where I was on my iPhone when I leave my desk.

Anyone having this same problem / know of a fix?

Thanks