Did you lose some matches at 0 LP after getting in to silver 5 when you were protected from dropping?
from what I've read, LP gains and losses are determined by your MMR relative to your division. If you're experiencing larger losses than gains, it means your MMR is significantly below average for your division - the difference is meant to get you to where the game thinks you belong, faster. If you win more games than you lose, your LP may still drop but your MMR will rise. As it rises you'll notice this difference decrease, and if you keep it up long enough you'll eventually get back to even. If you don't win more than you lose, you'll eventually be relegated to bronze 1 and assuming your MMR matches in bronze 1 you'll have equal gains and losses.
a good way to verify this is to check what division people you're matched with are in. The overall average of each time should be about silver 5 if your MMR was average for silver 5. Since matching is based on MMR and you're experiencing this, I would assume your team on average is generally slightly above silver5 or your opponents slightly below. If the other 9 players your matched with are in bronze, it makes sense that you shouldn't gain as much for a win and lose more for a loss when in silver because you should be better than them.
The system is really poorly designed in my opinion. If you want to say you need to earn divisions via promos then stick to that and only adjust in the most extreme circumstances (rather than matchmaking on some behind the scenes basis). If you want a sliding scale, drop promo series and just base division directly off of MMR. CLARITY please :)
