Hi - I have a new podcast episode that went up this morning and it is showing in Spotify but not Apple. It is the Learning to Slay the Beasts podcast.
Your episode 55 was posted only today. It appears when subscribing (where the feed is read directly) but the iTunes Store/Apple Podcasts 'Browse' caches the feeds and visits them in some sort of rotation to check for updates. A delay of up to two days is quite common, occasionally more: it can be less - it depends on where you are in the cycle when you post. Generally, you can't expect a new episode to appear on the day it was posted.