Possible reasons of duplicates are:

1. More than one CopierEA was running on Source platform. For example, you have 2 charts on Source platform: EURUSD with SourceEA attached and GBPUSD chart on the same platform with SourceEA attached. 
   Please make sure that you have only one Copier EA (SourceEA or ReceiverEA) per one MT4 platform.
2. More than one CopierEA was running on Receiver platform. For example, you have 2 charts on Receiver platform: EURUSD with ReceiverEA attached and GBPUSD chart on the same platform with ReceiverEA attached.
   Please make sure that you have only one Copier EA (SourceEA or ReceiverEA) per one platform.
3. More than one instance of Provider/Processor MT4 platform logged into the same account were opened on this computer. This can happen on VPS when you have 2 sessions logged in.
   In this case just close the second Provider platform or restart the VPS.
4. You logged into the another account on Source side for some time and then logged into the previous account.
   Please disable EA execution (click AutoTrading button in MT4 platform) when you switch between accounts on Source or Receiver platforms.
5. You changed password in Source account and it caused MetaTrader to “re-login”. 
   ​​​​​​​Please disable EA execution (click “AutoTrading” button) when you change the password of Source account.