Why did this happen?

Well, it does appear so. But it seems like a stupid rule for correspondence chess; in my situation what am I supposed to do? Not prepare it at all when most of my opponents are booked up to move 30? None of you are factoring in my tournament at all. Anyways I also don't have an alternate solution so I don't know what to say.

This post will soon be locked!
In before the lock, I am very surprised "how Lichess detect the background engine is running in a single game"?

I thought cheating will be detected only after "several almost perfect games or with similar time usage regardless of difficulty of position"

I understand your point, @Koustav123456. But would you like to play versus engines in your correspondence games? If not, what do you suggest our rules against engine cheating in correspondence should be?

@thibault Actually it isn't that bad compared to playing against an engine on a blitz game. Of course, you will be pissed because you won't win but you can maybe learn more from a perfect player? I don't mind losing if I learned something.

Honestly I don't have any solution. Lichess seems to have a system of real human correspondence chess, compared to the actual engine correspondence chess as is common in for example, ICCF. In these circumstances, it's very difficult to differ between preparation for a real game and just pure cheating. But I guess you could at least let a mod check the game first; I mean who actually cheats after just 7 moves anyways :).

Anyways this also is probably a rare occurence, as it doesn't appear that many people play correspondence and play in serious OTB tournaments, and also many lower level players probably don't use the engine to prepare. Honestly I made this post only because I felt insulted that it said 'cheat detected' when to myself, I never really cheated in a true sense of the word.

Well, you have plenty of choices.
1) Not playing correspondence on lichess.
2) Not playing your usual opening repertoire in lichess correspondence.
3) Accept the fact that in one line (or how many correspondence games you play) out of hundred you need to use your brain for prep (until some moves are made in a game) rather than engine, while using engine in other lines. This was totally acceptable for me while playing Atomic World Championship, for example, because overall this hardly affects prep quality at all.
4) Playing Casual correspondence and agree with your opponent that it is OK to use engine in the opening whatever definition of opening you choose.
But violating the site rules because of some inconvinience for OTB play is not a solution, it's only a way to get banned.

Correspondence board have already the analysis tool with the evaluation off if you want to test lines....
Just wonder why you need the evaluation to "read''the position ?

Let me ask a question to clarify things. @Koustav123456 were you analyzing the same game with the engine? In other words, was the position you were anayzing related to the game you were playing at the same time?

Yeah basically when I was playing the game, I remembered that I needed to check this line as it was important in the Najdorf. Then I started analyzing it. So yes it was related. And #26, that does seem rather fair. I should have perhaps thought about those things a bit beforehand. But I just wanted to play my repertoire so that I got some practice.

If you preparing for your games why play correspondence which games might last forever?, why not play blitz or rapid and afterwards analyze using engines? , i dont think it makes sense playing a correspondence game while you also playing in a tournament, what if your opponent makes only 3 moves then logs off and comes back again in 2 days?, how will you prepare for the tournament?, maybe you should play short time controls then analyze later