Why is soloQ so feed intensive?

My MMR must be wrecked because heres the meme. I play 5 flex games practicing JG and some norms. I win every single one and no one on my team feeds. I play 3 solo/duo games. 2 of them every lane lost and fed at least 1-5. The one where my team didn't int riot gave me 468ms even though my PC showed that my internet connection from the ISP, to my router and to my PC were fine. It also showed no loss when travelling to WoW, Google or Discord. It was literally on LoL that was lagging. Then after that single match, no more lag. Magic.

My point being, how can I play flex/norms with no issue but the second I click solo/duo my team feeds and riot lag switches my account lol. 3 laners going 1-5 with their JG not ganking can't be my fault. Neither is the riot lag bs. Did I play like a challenjour? No but I also didn't deserve to lose 67LP because of things I can't control.

It also makes it so I cannot practice. If I practice with bots I go 30-0 and don't learn anything. If I practice in norms I just face-roll troll picks, if I play flex queue my team won't feed/int so we win. The only queue that my team consistently feeds in is SoloQ so I can't practice winning that without practicing in SoloQ. Like jesus.