[GAMEPLAY] Bots stuck on Nexus

So I hopped into a custom game today to try some things, and I immediately noticed that both Nasus Bot and Karthus Bot appeared to get stuck on our Nexus? They were stuck there for the first 19 or so minutes of the game, after which they finally got unstuck and went to lanes as per normal.

I'm wondering what caused this? It's most likely a one off bug but I'm curious is all.

also my apologies if the picture doesn't work it's my first time using one :'0