Got very low lp for a victory - normally around 20lp

Good Riot, Last evening I was playing a game with 0lp in G5. We won the game, but a the graphs screen my client was unable to connect so I had to exit. Once I opened the client, I could see that I only got 8lp for the victory. Normally I get around 17 to 21lp. I have been playing in G5 for a while, been in promos, back to zero etc. How come I suddenly get so low lp? Was it a bug?
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