I noticed this problem. I’m testing the expert Advisor on history. Modelling quality 90%. I change 1-2 parameters in the Expert Advisor, run them again. I get Modeling quality n/a. And this is on a day off, when no new quotes are delivered. You have to delete the entire history and download the archive again. Again 90%. Again I change some parameters of the Expert Advisor, run it and again n/a. I have seen this problem many times on different computers and in different DC terminals, but for some reason it is not constant. There are periods of several days when it is literally impossible to test. And it happens that everything is fine for a month. What is it, how can it be explained? How to deal with it? If you advise me to work with tick data, then in vain: exactly the same thing happens to them. Once run – 100%. The second time in a minute drove-90% and each time worse and worse.