The reason of this error may be either due to the works on the server (we warn players in advance in our official groups) or due to unstable internet connection.
Remember that the closer you are to server the better connection will be.
We recommend you to check your ping to Amsterdam (Europe) or Singapore (Asia), depending on where your server is located. It shouldn't be higher than 300 ms.
Close background apps that can load your internet connection.
Clean RAM and check if the game conflicts with antivirus.
If the error appears again, please, contact technical support.
Don't forget to write ID of the battle where error occurred.