As far as the official records go, ranked flex does not impact your solo queue matchmaking rating or MMR. ... As a result, a player can reach Diamond rank in flex with his friends but remain in Gold in his solo queue rank.

Does solo MMR affect Flex?

When you are in placements, you can't lose any LP when you lose games, which may have been what you experienced, otherwise, it's a bug and be happy. Flex MMR does not affect other queues MMR.

Can you play ranked Flex alone?

Flex Queue is a queue for competitive groups in League of Legends. In Flex Queue, players can queue solo or with groups of two, three, or five. Its ranking system is different from the dynamic queue ranking. Players can earn ranked rewards from Flex Queue at the end of a season.