I do find your information about these swings quite interesting. You appear to have a very seasoned account (XP level 300+) so seeing these swings is curious.
I strongly recommend taking the time to document the next few games, try to think about what heroes/role you are playing. Make any notable events of each match (leavers, your general performance, etc.). Maybe there might be a pattern.
That being said, I strongly encourage anyone to read the full details of how SR can fluctuate from this guide: