who is sending all the 120-140 satoshi/byte transactions? In the last few weeks, the mempool size has grown significantly. You can see with a mempool fee viewer such as this one that overwhelmingly, transactions are growing at the 120-140 satoshis/byte fee range. 

Why would this particular level grow so much faster than any other level? Is there any activity that is more likely to be in these transactions? (like sending money to exchanges, activity from certain wallets, certain blockchain services, etc...?)
I noticed that blockchain.info wallets recommend fees in the 120-140 s/B range. I've been manually increasing my fee to ensure my transaction gets confirmed by checking https://bitcoinfees.21.co/ when I send money anywhere. 

I would assume there is simply an error in how blockchain.info and potentially other wallets are calculating the appropriate fee.