All Issued Movement Commands Are Directed Towards The Enemy Nexus

Server: NA

Type of Bug: in-game bug

Description: When entering a new game, the game was severely lagging for a full minute. Once the game stopped lagging, I bought my items just fine, but when I closed the shop window my mouse cursor was gone. I would click to bot lane but the click would register on the enemy nexus. Wherever I clicked my champion walked down midlane towards the enemy nexus. I tried to open the options menu but my mouse cursor appeared on the exact center of the screen and would not move. I could not click anything on the menu. I unplugged/replugged my mouse to no avail. I alt+tabbed then reopened the game to find my mouse cursor was back to normal. My movement commands still went towards the enemy nexus, but I was able to click buttons on the menu. After disconnecting/reconnecting, the bug was gone.

Video / Screenshot: None

Steps to reproduce: Not sure. I was playing Janna in ranked.

Expected result: Champion moves towards where I right click.

Observed result: Champion moves towards the enemy nexus down midlane.

Reproduction rate: Wasn't able to reproduce.

System specs: Windows 7. Intel Celeron processor.

I would like to note that since a few patches back, I've had lagging in the first 1 or 2 minutes of the game, and at the end of every game. It's been happening literally every game. However it's never lead to any major bugs like this before.