There has been a new issue introduced in Instacast 2.0.1 that persists in Instacast 2.1 which could cause subscriptions to not load new episodes.
In most cases you can reach the same podcast over different URLs. One example would be a URL using a domain and one using the server ip. In order for Instacast to match these cases it uses redirect URLs and the rel=self URL in the feed.
However there can be cases where this method fails, e.g. when the publishers gives a false URL in the rel=self URL. Then Instacast changes the internal URL and fails to reload the feed next time.
I am currently investigating a workaround.