Fps drops from around 6-7min to 12-13min

So I am having this problem every single game from min 6-7 to min 12-13 (sometimes it starts at min 6,sometimes 7 and lasts for 4-5 mins you get the point) my fps suddenly drops to 20-30 for no reason at all and there is also some game freeze from time to time in that period... As I saw some other threads I am not the only one having this problem,and before you say or suggest it that its something running in the background and making my pc lag - Noop, its not.I have checked the processes and nothing seems to be the cause of it. So it basicly gets me to a period of 4-5 mins where best I can do is hope to hit skill shots and not fail things because of the fps drop and random lag that makes the game kinda unplayable.After that period of time it gets back to normal,but to be honest its a huge problem,since in most of the games that time period is probably the most important one at least for the lane phase. This problem started like 2 or 3 patches ago at least for me,and what makes it more interesting as I noticed it only occurs in 5v5 ranked and normal games ( not sure about 3v3),but however when I played the URF mode the fps drop wasnt happening.As I said only in normal and ranked 5v5 games. I basicly tried to repair the game and every other advice I could find on the threads but nothing helped. Just want to point out that there is this fps drop problem and its happening to a lot of people for a week or two and if you could fix it,we would be thankful. P.S. Dont say its Avast or something similar I am not even using that.
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