Siri can't switch between podcast/music

I'm having trouble with getting Siri to switch between content.

My phone is unlocked and I'm playing music. I decide I want to listen to a podcast.

I ask Siri "Play last podcast"

Her screen shows "playing all podcasts" --- but nothing happens?

Same thing happens in reverse. If I'm playing a podcast and ask "shuffle all songs" -- I get "playing all songs, shuffled..." but nothing happens.

What's going on?

If I ask to switch between albums say (staying in the same app) it works fine.

Thanks!