diff --git a/src/main/java/dev/loki/loparkour/generator/core/coordinator/GeneratorProfileManager.java b/src/main/java/dev/loki/loparkour/generator/core/coordinator/GeneratorProfileManager.java
index ec189fa..e2dfd9f 100644
--- a/src/main/java/dev/loki/loparkour/generator/core/coordinator/GeneratorProfileManager.java
+++ b/src/main/java/dev/loki/loparkour/generator/core/coordinator/GeneratorProfileManager.java
@@ -130,7 +130,12 @@ public class GeneratorProfileManager {
                 String materialName = Config.GENERATION.getString(materialPath);
                 int chance = Config.GENERATION.getInt(chancePath, 1);
 
-                BlockData blockData = org.bukkit.Bukkit.createBlockData(materialName);
+                BlockData blockData;
+                try {
+                    blockData = org.bukkit.Bukkit.createBlockData(materialName);
+                } catch (IllegalArgumentException e) {
+                    continue; // skip invalid material names
+                }
                 generator.state.specialChances.put(blockData, (double) chance);
             }
 
diff --git a/src/main/java/dev/loki/loparkour/generator/core/model/GeneratorState.java b/src/main/java/dev/loki/loparkour/generator/core/model/GeneratorState.java
index 33c3cee..4e45f59 100644
--- a/src/main/java/dev/loki/loparkour/generator/core/model/GeneratorState.java
+++ b/src/main/java/dev/loki/loparkour/generator/core/model/GeneratorState.java
@@ -31,8 +31,9 @@ public class GeneratorState {
     // Time state
     public Instant start;
 
-    // Block history (sync list: all mutations occur on the main thread; avoids accidental CME if extended later)
-    public final List<Block> history = Collections.synchronizedList(new LinkedList<>());
+    // Block history — all access is main-thread-only (Bukkit scheduler runTimer), so no sync wrapper needed.
+    // Iteration is safe without external synchronization as all mutations happen on the same thread.
+    public final List<Block> history = new ArrayList<>();
     public int lastPositionIndexPlayer = -1;
 
     // Schematic state
diff --git a/src/main/java/dev/loki/loparkour/generator/core/model/Profile.java b/src/main/java/dev/loki/loparkour/generator/core/model/Profile.java
index 4629f94..c1e21b6 100644
--- a/src/main/java/dev/loki/loparkour/generator/core/model/Profile.java
+++ b/src/main/java/dev/loki/loparkour/generator/core/model/Profile.java
@@ -45,16 +45,18 @@ public class Profile {
         }
 
         /**
-         * @return The value as a double.
+         * @return The value as a double. Returns 0.0 if the value is empty.
          */
         public double asDouble() {
+            if (value.isEmpty()) return 0.0;
             return Double.parseDouble(value);
         }
 
         /**
-         * @return The value as an int.
+         * @return The value as an int. Returns 0 if the value is empty.
          */
         public int asInt() {
+            if (value.isEmpty()) return 0;
             return Integer.parseInt(value);
         }
     }
diff --git a/src/main/java/dev/loki/loparkour/generator/jump/placement/BlockSelector.java b/src/main/java/dev/loki/loparkour/generator/jump/placement/BlockSelector.java
index af09e0c..2d2c65f 100644
--- a/src/main/java/dev/loki/loparkour/generator/jump/placement/BlockSelector.java
+++ b/src/main/java/dev/loki/loparkour/generator/jump/placement/BlockSelector.java
@@ -9,6 +9,8 @@ import org.bukkit.block.data.BlockData;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.List;
+
 /**
  * Handles selection of block types and materials for parkour generation.
  */
@@ -29,7 +31,11 @@ public class BlockSelector {
     public BlockData selectBlockData() {
         Style style = Registry.getStyle(generator.profile.get("style").value());
         if (style == null) {
-            generator.profile.set("style", Registry.getStyles().stream().findFirst().orElseThrow().getName());
+            List<Style> styles = Registry.getStyles();
+            if (styles.isEmpty()) {
+                return Material.STONE.createBlockData();
+            }
+            generator.profile.set("style", styles.stream().findFirst().orElseThrow().getName());
             return selectBlockData();
         }
         for (int i = 0; i < MAX_STYLE_PICKS; i++) {
diff --git a/src/main/java/dev/loki/loparkour/generator/lifecycle/loop/LifecycleTickManager.java b/src/main/java/dev/loki/loparkour/generator/lifecycle/loop/LifecycleTickManager.java
index 563dc96..d56b838 100644
--- a/src/main/java/dev/loki/loparkour/generator/lifecycle/loop/LifecycleTickManager.java
+++ b/src/main/java/dev/loki/loparkour/generator/lifecycle/loop/LifecycleTickManager.java
@@ -92,7 +92,8 @@ public class LifecycleTickManager {
         
         if (currentBlocks < targetBlocks) {
             int needed = targetBlocks - currentBlocks;
-            generator.generate(needed);
+            // Cap generation per tick to prevent runaway generation in multiplayer
+            generator.generate(Math.min(needed, 5));
         }
     }
 }
diff --git a/src/main/java/dev/loki/loparkour/generator/lifecycle/player/PlayerInteractionHandler.java b/src/main/java/dev/loki/loparkour/generator/lifecycle/player/PlayerInteractionHandler.java
index 15d4e38..0e95fee 100644
--- a/src/main/java/dev/loki/loparkour/generator/lifecycle/player/PlayerInteractionHandler.java
+++ b/src/main/java/dev/loki/loparkour/generator/lifecycle/player/PlayerInteractionHandler.java
@@ -82,8 +82,8 @@ public class PlayerInteractionHandler {
             }
         }
 
-        // Generate more blocks after scoring
-        generator.generate(1);
+        // Block generation is handled by LifecycleTickManager.maintainBlockLead()
+        // to avoid runaway generation in multiplayer (N players = N generates per tick otherwise).
     }
     
     /**