I noticed a lot of Proof of Stake blocks with 3xmg only, in block chain explorer. Is this normal?
Yes. it's a function of the blockchain. after a string of large payouts the chain tries to lower the number of findable blocks by prioritising Staking over mining.
so it lowers the limit of staking from around 50/100xmg down to as little as 3xmg to help balance the chain. (ideally the block at the end should be made up of 75% staking rewards to 25% mining.).
Once it calms down the staking limit will rise again.