I have experienced this for quite some time so I believe this is not a temporarily problem e.g. network. I am using Chrome browser and when I publish a post, it shows: 'Transaction broadcast error'
But actually, the post is already published, so If I press Post after sometime, e.g. 5 minute limitation between any two posts, there will be a duplicate post pushed to the steem blockchain.
Here is the error message when I press F12 in the Chrome console, which helps to identify this problem.
This happens every time on my PC, here is my browser:
