It may be several reasons (broker deleted the history, abnormal monthly growth, and so more).
abnormal growth is ignored by the system - look at this post #6

Signals - Reliability
- 2018.12.07
- www.mql5.com
How do I understand the Reliability Index for Signal providers...
Thanks for your reply Sergey.
I'm not selling signals or anything. I have all my history data available from day one. This is just a new account that only have three weeks life so far. I'm using this to see how my EA is doing.
Its just weired the number doesnt make sense. But thanks anyways.im going back to myfxbook.

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Hello there,
I have set up my own private signal to see the trading stats.
My account started trading on June 1, but for some reason, system only loaded trades from June 15th.
Profit is around 2500, and initial deposit 10000, so the growth should be 25% instead of only 9% as it shows.
What's wrong here?
Thanks guys.