user12953: I've noticed that the engine (Stockfish 9) evaluates positions as significantly better for white if the evaluation is performed while white is on the move. The difference is sometimes more than half a point.
Someone else has noticed this phenomenon, and anyone has an idea what the reason is (It's not run time, as I've let the engine evaluate above 26 PLY in both cases).
To clarify: The intention here is NOT the same position, just switching who's on the move. I will examplify by the start position. Imagine evaluating it and the engine gives +0.7 and gives the 1. e4 e5. Then you make the move 1.e4 and let the engine evaluate again, and now it gives only +0.2 and recommends 1.. e5.

user12953: So, basically the answer is like this:
Let's say the engine analyzes the start position at 30 PLY and recommends 1. e4 with a score of +0.7 for white. Once I made the move 1. e4 and let the engine analyze the new position to the same depth (29 PLY) it would well evaluate the position differently and give it a score of only +0.2. The reason for this is that the engine now examines more of the leafs starting with 1. e4 than it did from the start position (since it now disregards all branches starting with other first moves), and thus performs a deeper analysis (more leaves) of this branch even though it goes no further in number of moves.

user825: There's nothing surprising here. Chess engine is not perfect, as you make a move the evaluation will likely change:

The engine now sees something not seen before
The engine can now search deeper
The engine's hash table has relevant entries

This's just how we play chess. Our positional assessment change as we make moves. If that's not the case, there's no need to play the game - we shout out win/loss/draw without making a move.
Hint: If you're using your engine for your game, you'll need to make some moves to get better assessment. Kramnik did that for his win against Aronian:

The computer doesn’t show it at the beginning, but then once you put it in he starts to like it a lot. 

https://chess24.com/en/read/news/berlin-candidates-3-a-kramnik-immortal
Sorry, chess is a hard game.

user16827: Try to set 'contempt' to 0. Had the same problem, this solved it for me.

12953: <p>I've noticed that the engine (Stockfish 9) evaluates positions as significantly better for white if the evaluation is performed while white is on the move. The difference is sometimes more than half a point.</p>

<p>Someone else has noticed this phenomenon, and anyone has an idea what the reason is (It's not run time, as I've let the engine evaluate above 26 PLY in both cases).</p>

<p>To clarify: The intention here is NOT the same position, just switching who's on the move. I will examplify by the start position. Imagine evaluating it and the engine gives +0.7 and gives the 1. e4 e5. Then you make the move 1.e4 and let the engine evaluate again, and now it gives only +0.2 and recommends 1.. e5.</p>
 12953: <p>So, basically the answer is like this:
Let's say the engine analyzes the start position at 30 PLY and recommends 1. e4 with a score of +0.7 for white. Once I made the move 1. e4 and let the engine analyze the new position to the same depth (29 PLY) it would well evaluate the position differently and give it a score of only +0.2. The reason for this is that the engine now examines more of the leafs starting with 1. e4 than it did from the start position (since it now disregards all branches starting with other first moves), and thus performs a deeper analysis (more leaves) of this branch even though it goes no further in number of moves.</p>
 825: <p>There's nothing surprising here. Chess engine is not perfect, as you make a move the evaluation will likely change:</p>

<ul>
<li>The engine now sees something not seen before</li>
<li>The engine can now search deeper</li>
<li>The engine's hash table has relevant entries</li>
</ul>

<p>This's just how we play chess. Our positional assessment change as we make moves. If that's not the case, there's no need to play the game - we shout out win/loss/draw without making a move.</p>

<p>Hint: If you're using your engine for your game, you'll need to make some moves to get better assessment. Kramnik did that for his win against Aronian:</p>

<blockquote>
  <p>The computer doesn’t show it at the beginning, but then once you put it in he starts to like it a lot. </p>
</blockquote>

<p><a href="https://chess24.com/en/read/news/berlin-candidates-3-a-kramnik-immortal" rel="nofollow noreferrer">https://chess24.com/en/read/news/berlin-candidates-3-a-kramnik-immortal</a></p>

<p>Sorry, chess is a hard game.</p>
 16827: <p>Try to set 'contempt' to 0. Had the same problem, this solved it for me.</p>
