transactions are not getting mined on rinkeby testnet and last block time is almost 2 hours ago. How did such things happen in a decentralised network?
Well it is a testnet.
Without knowing what has happened here are some alternatives:
1) Some new network feature is being tested and it didn't work out very well (unlikely option)
2) There simply aren't enough validators online
3) The tools I (we?) use to check the status are malfunctioning
4) Some other malfunction in the network. Unlikely.
Testnets are meant for testing and they may have this kind of oddities every now and then. It doesn't have too much to do with the decentralized nature of the network.
I checked https://www.rinkeby.io/#stats a few minutes ago.
There was a problem with validators. To few were online.
Now it runs again.