From c73f21df97e98c960773d0eb0fcf765582c06fed Mon Sep 17 00:00:00 2001
From: pb00067 <pb00067@phxl0401.wp.lan>
Date: Sat, 22 Nov 2025 13:24:03 +0100
Subject: [PATCH] Fix for SF getting stuck during search (issue #5023)

Among several passed similar versions this is the simpliest one.

Passed STC non-regression
https://tests.stockfishchess.org/tests/view/691f3b4aacb6dbdf23d07d11
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 126368 W: 32607 L: 32489 D: 61272
Ptnml(0-2): 408, 13974, 34298, 14100, 404

Passed LTC non-regression
https://tests.stockfishchess.org/tests/view/69209712acb6dbdf23d0836a
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 114786 W: 29097 L: 28976 D: 56713
Ptnml(0-2): 53, 11841, 33488, 11954, 57

closes https://github.com/official-stockfish/Stockfish/pull/6447

Bench: 2941767
---
 src/search.cpp | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/search.cpp b/src/search.cpp
index d2a90283c..9924b0cec 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -141,6 +141,16 @@ void update_all_stats(const Position& pos,
                       Move            TTMove,
                       int             moveCount);
 
+bool isShuffling(Move move, Stack* const ss, const Position& pos) {
+    if (type_of(pos.moved_piece(move)) == PAWN || pos.capture_stage(move)
+        || pos.rule50_count() < 10)
+        return false;
+    if (pos.state()->pliesFromNull <= 6 || ss->ply < 20)
+        return false;
+    return move.from_sq() == (ss - 2)->currentMove.to_sq()
+        && (ss - 2)->currentMove.from_sq() == (ss - 4)->currentMove.to_sq();
+}
+
 }  // namespace
 
 Search::Worker::Worker(SharedState&                    sharedState,
@@ -1114,7 +1124,7 @@ moves_loop:  // When in check, search starts here
         // and lower extension margins scale well.
         if (!rootNode && move == ttData.move && !excludedMove && depth >= 6 + ss->ttPv
             && is_valid(ttData.value) && !is_decisive(ttData.value) && (ttData.bound & BOUND_LOWER)
-            && ttData.depth >= depth - 3)
+            && ttData.depth >= depth - 3 && !isShuffling(move, ss, pos))
         {
             Value singularBeta  = ttData.value - (53 + 75 * (ss->ttPv && !PvNode)) * depth / 60;
             Depth singularDepth = newDepth / 2;