I guess it is due to lower transaction fee, I just noticed that any transaction less than 200s.byte will be possibly confirmed on the next 25 blocks, mostly the one that is instantly confirmed are the one that sent a transaction of 400+ sat/ byte.  There is a sudden increase in transaction fee and this time it is actually insane.  

Currently, most of my fee is 400/byte and I still need to wait more than 1 day for my transaction to be confirmed. Your fee is only 160 satoshi/byte. well, I think it will stuck there for whole week

The wallet (or service) that you used to send the transaction did not calculate a high enough transaction fee. Transactions that paid a higher fee-per-byte than you are getting confirmed instead of your transaction.

What wallet or website did you use to send the transaction?