This has been in since the previous preseason patch but I haven't seen much discussion about it. Creep block has been noticeably worse ever since the preseason patch came out. At first I thought it was just due to me making poor decisions with my character movements but after playing more games I've figured out that something is definitely different.
The most noticeable difference in creep blocking is the way you move when three or more mage minions are in a line or clumped together. In the previous patch if mage minions were clumped together you would generally move between two of them to get to wherever you clicked. Instead of that, you now path around minions which takes longer to get to where you were going and may occasionally screw you over in some certain situations, whether it be missing a CS or taking some slight unnecessary damage.
The pathing with creep blocking has gotten so bad that when I was in a bot game, my character pathed all the way to the opposite side of the enemy nexus because I couldn't move between the line of minions that were attacking it. It's just a really annoying bug and I'd like to bring attention to it.