This is happening to me too, and it's super frustrating. Here's how I would explain the problem. I spend a lot of time deciding which episodes I want to listen to next, and making sure they're in the order I want them. And I put my favorites up top, and the ones that I'm not quite as into down lower, so that I always have a nice long queue. A year ago, if I accidentally ever clicked Play on anything, it would ask me a question something like "After playing this episode what do you want to do? Keep Up Next or Clear Up Next." And I had to be careful not to clear my Up Next queue.
It seems that the behavior changed a few months ago, and now the question doesn't get asked - it just always clears the queue. As if there was a default setting which you can't change.
This mostly happens to me when I first open my phone, wake it up, and quickly play my podcasts. Or if I'm using my Airpods. If I press play from the home screen without first opening the podcast app and making sure that the one I was listening to is there and make sure my Up Next queue is displayed everything will get wiped out.
I got so frustrated the other day that I tried to rebuild my library and queue in both the Audible and Spotify podcast sections, but neither of those worked as well as Apple's native Podcast app, so I gave up.
A friend of mine suggested switching to Overcast. I'm going to upgrade to iOS 15.2 today, and if my queue deletes again, I'll download and install Overcast. I hope that this is an issue Apple is aware of and is fixing.
