Podcast episodes have disappeared

The feed seems to be fine and as you say works perfectly well when subscribing, so it's difficult to say what is going on. The Store can be flaky sometimes, though usually it takes the form of claiming to be showing the correct number of episodes but not actually showing any. Otherwise if could happen if you had done something temporarily to your feed which caused there to be no episodes in it, and the Store happened to check it while it was in that condition. In that case the episodes would reappear on the next check; if it's a glitch it may correct itself in the same way.

As your feed is OK there isn't really anything you can do aobout it - you could try emailing Support at podcasts 'at' apple.com but their level of helpfulness is very variable and you may just get a form answer telling you how to add episodes, which you already know. You've nothing to lose by trying, of course.