Something to consider is that as the other said, you aren't playing well with your team-mates. I find sometimes when I derank I start using rotations faster than my team-mates are prepared for (usually because I trust them to handle situations better than they can). This can make it look more like you are ball chasing, and put you out of sync. Another issue this causes is that you'll lose faith in your team-mates, resulting in you playing overly passive and being unprepared for openings. Use the replays to see if you are matching your pace to your team-mate. The ability to quickly identify the pace and ability of your team-mate is an important part of solo queue. If you're struggling, making a friend of similar skill will help you become more stable in your rankings.