Weired MMR in high plat

So I have been grinding A TON in the last week , what I observed was , that as soon as i promoted to Plat 2 I played with D5-D3 only , but when I demoted back to Plat3 (literally from 1 game to another) I played with Gold 1 and even Silver 1's Is that kind of jump in MMR usual or common ?
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