diff --git a/osu.Game.Tests/Database/BackgroundDataStoreProcessorTests.cs b/osu.Game.Tests/Database/BackgroundDataStoreProcessorTests.cs
index e65088ca2ed1..43ce7200d28f 100644
--- a/osu.Game.Tests/Database/BackgroundDataStoreProcessorTests.cs
+++ b/osu.Game.Tests/Database/BackgroundDataStoreProcessorTests.cs
@@ -127,8 +127,11 @@ public void TestDifficultyProcessingWhilePlaying()
             });
         }
 
+        [TestCase(30000001)]
         [TestCase(30000002)]
         [TestCase(30000003)]
+        [TestCase(30000004)]
+        [TestCase(30000005)]
         public void TestScoreUpgradeSuccess(int scoreVersion)
         {
             ScoreInfo scoreInfo = null!;
diff --git a/osu.Game/BackgroundDataStoreProcessor.cs b/osu.Game/BackgroundDataStoreProcessor.cs
index d4cd1ff6ea99..8f6dced350df 100644
--- a/osu.Game/BackgroundDataStoreProcessor.cs
+++ b/osu.Game/BackgroundDataStoreProcessor.cs
@@ -316,8 +316,7 @@ private void convertLegacyTotalScoreToStandardised()
 
             HashSet<Guid> scoreIds = realmAccess.Run(r => new HashSet<Guid>(r.All<ScoreInfo>()
                                                                              .Where(s => !s.BackgroundReprocessingFailed && s.BeatmapInfo != null
-                                                                                                                         && (s.TotalScoreVersion == 30000002
-                                                                                                                             || s.TotalScoreVersion == 30000003))
+                                                                                                                         && s.TotalScoreVersion < LegacyScoreEncoder.LATEST_VERSION)
                                                                              .AsEnumerable().Select(s => s.ID)));
 
             Logger.Log($"Found {scoreIds.Count} scores which require total score conversion.");
diff --git a/osu.Game/Database/StandardisedScoreMigrationTools.cs b/osu.Game/Database/StandardisedScoreMigrationTools.cs
index 6484500bcc76..d2321f4fc48e 100644
--- a/osu.Game/Database/StandardisedScoreMigrationTools.cs
+++ b/osu.Game/Database/StandardisedScoreMigrationTools.cs
@@ -26,7 +26,7 @@ public static bool ShouldMigrateToNewStandardised(ScoreInfo score)
             if (score.IsLegacyScore)
                 return false;
 
-            if (score.TotalScoreVersion > 30000004)
+            if (score.TotalScoreVersion > 30000002)
                 return false;
 
             // Recalculate the old-style standardised score to see if this was an old lazer score.
@@ -293,13 +293,23 @@ public static long ConvertFromLegacyTotalScore(ScoreInfo score, LegacyBeatmapCon
                     // Roughly corresponds to integrating f(combo) = combo ^ COMBO_EXPONENT (omitting constants)
                     double maximumAchievableComboPortionInStandardisedScore = Math.Pow(maximumLegacyCombo, 1 + ScoreProcessor.COMBO_EXPONENT);
 
-                    double comboPortionInScoreV1 = maximumAchievableComboPortionInScoreV1 * comboProportion / score.Accuracy;
-
                     // This is - roughly - how much score, in the combo portion, the longest combo on this particular play would gain in score V1.
                     double comboPortionFromLongestComboInScoreV1 = Math.Pow(score.MaxCombo, 2);
                     // Same for standardised score.
                     double comboPortionFromLongestComboInStandardisedScore = Math.Pow(score.MaxCombo, 1 + ScoreProcessor.COMBO_EXPONENT);
 
+                    // We estimate the combo portion of the score in score V1 terms.
+                    // The division by accuracy is supposed to lessen the impact of accuracy on the combo portion,
+                    // but in some edge cases it cannot sanely undo it.
+                    // Therefore the resultant value is clamped from both sides for sanity.
+                    // The clamp from below to `comboPortionFromLongestComboInScoreV1` targets near-FC scores wherein
+                    // the player had bad accuracy at the end of their longest combo, which causes the division by accuracy
+                    // to underestimate the combo portion.
+                    // Ideally, this would be clamped from above to `maximumAchievableComboPortionInScoreV1` too,
+                    // but in practice this appears to fail for some scores (https://github.com/ppy/osu/pull/25876#issuecomment-1862248413).
+                    // TODO: investigate the above more closely
+                    double comboPortionInScoreV1 = Math.Max(maximumAchievableComboPortionInScoreV1 * comboProportion / score.Accuracy, comboPortionFromLongestComboInScoreV1);
+
                     // Calculate how many times the longest combo the user has achieved in the play can repeat
                     // without exceeding the combo portion in score V1 as achieved by the player.
                     // This is a pessimistic estimate; it intentionally does not operate on object count and uses only score instead.
diff --git a/osu.Game/Scoring/Legacy/LegacyScoreEncoder.cs b/osu.Game/Scoring/Legacy/LegacyScoreEncoder.cs
index 00b1f04782e5..5c51e68d9f58 100644
--- a/osu.Game/Scoring/Legacy/LegacyScoreEncoder.cs
+++ b/osu.Game/Scoring/Legacy/LegacyScoreEncoder.cs
@@ -32,9 +32,10 @@ public class LegacyScoreEncoder
         /// <item><description>30000003: First version after converting legacy total score to standardised.</description></item>
         /// <item><description>30000004: Fixed mod multipliers during legacy score conversion. Reconvert all scores.</description></item>
         /// <item><description>30000005: Introduce combo exponent in the osu! gamemode. Reconvert all scores.</description></item>
+        /// <item><description>30000006: Fix edge cases in conversion after combo exponent introduction that lead to NaNs. Reconvert all scores.</description></item>
         /// </list>
         /// </remarks>
-        public const int LATEST_VERSION = 30000005;
+        public const int LATEST_VERSION = 30000006;
 
         /// <summary>
         /// The first stable-compatible YYYYMMDD format version given to lazer usage of replays.