I will send the logs to get checked by the riots.
Can you please add your .rpd performance logs to this post the next time you have an issue? Please also include the replay from the offending game, and some notes on the game time when you had the issue. On my computer, the logs are located here:
C:\Riot Games\League of Legends\Logs\Performance Logs
We can analyze those logs and compare them to the replay to see exactly what was causing the performance slowdown. We really want to tackle these perf problems, so thank you in advance for posting about it!