When you import your podcast via OPML, we use the RSS feed that's provided in the OPML file. If a podcast is imported as private, that means that we could match it with our database of public podcasts. In rare cases, it occurs that the feed URL from your OPML is just different and couldn't be matched. If this occurs, the best is to search for the podcast and subscribe to the public version you can find with the Snipd search.