Like many others my scroll wheel started randomly reversing after a few months. I was going to attempt to do: https://www.reddit.com/r/MouseReview/comments/6yat7s/g703g403_random_scrolling_bug_fix/ but I realized that was not the issue(at least in my case).
I use my scroll wheel as a middle click a lot and after doing some tests with the encoder I found the problem. I believe the scroll wheel's tube that goes into the encoder got loose due to my heavy usage of the middle click. My fix was to put the scroll wheel and the encoder closer together. This is done by shaving off some plastic that keeps it apart and wedging a piece of paper so the encoder tilts closer towards the scroll wheel
I'
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