yeah I've seen this happen, the problem is the actual bounding box of the units, I think the hitboxes are actual boxes, meaning that they are invisible cubes that surround every unit, when the minions position themselves in an arc formation, in between cubes appear these angled corner like empty spaces that are accessible so the game paths you through it, the other side though is too narrow for your own hitbox to go through, this results in the minions either being pushed away a little or you being denied entry, what happens in game is a bit of both.
The problem, and the actual creep block, happens when one of the minions moves a little and your own hitbox is squished in between both of their hitboxes, the path that was there a while ago in the shape of an angled corner is now a hallway that's too narrow for you to fit in, so you can't get out of there until one of the hitboxes is cleared.
The solution to this is probably incresing minion's hitboxes size, that way you reduce "angled corner spaces" in between them but there will ALWAYS be a chance for someone to get stuck so Riot would need to implement some kind of AI where minions recognize each others proximity and react accordingly... naturally, this kind of technology takes time to code and we'd be very naive to think that they aren't actively working on a solution at this very moment.