Non reproducible test results

 
I am new user and I am testing few EAs. I have been able to optimize the EAs and received good results during back testing. I saved the input parameters and tried to run them again the other day and received completely different back testing results when testing again with the same settings. Any ideas how can it happen?
 
IYS:
I am new user and I am testing few EAs. I have been able to optimize the EAs and received good results during back testing. I saved the input parameters and tried to run them again the other day and received completely different back testing results when testing again with the same settings. Any ideas how can it happen?

Is it MT4 or MT5?

If MT4, do you use the same spread in tester? If it is set to "Current", it can cause the difference.

 
It is MT5
Reason: