Miners are unwilling to activate Constantinople or problems with updating the code base?
Firstly on 13 October mining in Ropsten network stopped on the block 4229999. This could be caused by the unwillingness of the miners to activate Constantinople or some other problems with the update of code base.
Finally, after two hours of waiting, first block with Constantinople activated was mined. Although after that many people felt relief, there were no transactions in the network. Seeing this situation, Ethereum developers started encouraging miners to maintain the stability of Ropsten.
Furthermore, Afri Schoendon, the developer of Ethereum client announced on Twitter that there was a consensus error in Ropsten, what led to triple fork between Geth, Parity and one more client.