You can vote or comment for this issue: Web socket events do not work. · Issue #3006 · input-output-hk/cardano-sl · GitHub
If you feel confident enough - you can check out these comments How to query based on Block-Height and listen to new Block/Transaction events | Also Sockets-API - #10 by _ilap and open a pull-request into the codebase that fixes the problem.
And use Web API in the meantime.