LP and MMR are like high ping.

LP is based on/a reflection of MMR, but it is often behind the 8 ball. Have you ever played with high ping on this game? You press a button and after a while later the result happens. The relationship between LP and MMR can be thought a bit like that. MMR issues the command and after a time delay LP results happen.

So when you are losing more LP than gaining its because of this desync. Your MMR is lower than the LP suggests and the LP is trying to follow, but lagging a little behind.