diff --git a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataBuildManager.java b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataBuildManager.java
index ebff6913..2c0a1a63 100644
--- a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataBuildManager.java
+++ b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataBuildManager.java
@@ -75,8 +75,12 @@ public class ArbitraryDataBuildManager extends Thread {
         if (now == null) {
             return;
         }
-        arbitraryDataBuildQueue.entrySet().removeIf(entry -> entry.getValue().hasReachedBuildTimeout(now));
-        arbitraryDataFailedBuilds.entrySet().removeIf(entry -> entry.getValue().hasReachedFailureTimeout(now));
+        synchronized (arbitraryDataBuildQueue) {
+            arbitraryDataBuildQueue.entrySet().removeIf(entry -> entry.getValue().hasReachedBuildTimeout(now));
+        }
+        synchronized (arbitraryDataFailedBuilds) {
+            arbitraryDataFailedBuilds.entrySet().removeIf(entry -> entry.getValue().hasReachedFailureTimeout(now));
+        }
     }
 
     // Build queue
diff --git a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileListManager.java b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileListManager.java
index 415e410c..b30dc092 100644
--- a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileListManager.java
+++ b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileListManager.java
@@ -84,7 +84,9 @@ public class ArbitraryDataFileListManager {
             return;
         }
         final long requestMinimumTimestamp = now - ArbitraryDataManager.ARBITRARY_REQUEST_TIMEOUT;
-        arbitraryDataFileListRequests.entrySet().removeIf(entry -> entry.getValue().getC() == null || entry.getValue().getC() < requestMinimumTimestamp);
+        synchronized (arbitraryDataFileListRequests) {
+            arbitraryDataFileListRequests.entrySet().removeIf(entry -> entry.getValue().getC() == null || entry.getValue().getC() < requestMinimumTimestamp);
+        }
     }
 
 
diff --git a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileManager.java b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileManager.java
index a529282c..b6559abd 100644
--- a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileManager.java
+++ b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileManager.java
@@ -101,14 +101,22 @@ public class ArbitraryDataFileManager extends Thread {
             return;
         }
         final long requestMinimumTimestamp = now - ArbitraryDataManager.getInstance().ARBITRARY_REQUEST_TIMEOUT;
-        arbitraryDataFileRequests.entrySet().removeIf(entry -> entry.getValue() == null || entry.getValue() < requestMinimumTimestamp);
+        synchronized (arbitraryDataFileRequests) {
+            arbitraryDataFileRequests.entrySet().removeIf(entry -> entry.getValue() == null || entry.getValue() < requestMinimumTimestamp);
+        }
 
         final long relayMinimumTimestamp = now - ArbitraryDataManager.getInstance().ARBITRARY_RELAY_TIMEOUT;
-        arbitraryRelayMap.removeIf(entry -> entry == null || entry.getTimestamp() == null || entry.getTimestamp() < relayMinimumTimestamp);
-        arbitraryDataFileHashResponses.removeIf(entry -> entry.getTimestamp() < relayMinimumTimestamp);
+        synchronized (arbitraryRelayMap) {
+            arbitraryRelayMap.removeIf(entry -> entry == null || entry.getTimestamp() == null || entry.getTimestamp() < relayMinimumTimestamp);
+        }
+        synchronized (arbitraryDataFileHashResponses) {
+            arbitraryDataFileHashResponses.removeIf(entry -> entry.getTimestamp() < relayMinimumTimestamp);
+        }
 
         final long directConnectionInfoMinimumTimestamp = now - ArbitraryDataManager.getInstance().ARBITRARY_DIRECT_CONNECTION_INFO_TIMEOUT;
-        directConnectionInfo.removeIf(entry -> entry.getTimestamp() < directConnectionInfoMinimumTimestamp);
+        synchronized (directConnectionInfo) {
+            directConnectionInfo.removeIf(entry -> entry.getTimestamp() < directConnectionInfoMinimumTimestamp);
+        }
     }
 
 
@@ -484,7 +492,9 @@ public class ArbitraryDataFileManager extends Thread {
     }
 
     private void removeFromRelayMap(ArbitraryRelayInfo entry) {
-        arbitraryRelayMap.removeIf(relayInfo -> relayInfo.equals(entry));
+        synchronized (arbitraryRelayMap) {
+            arbitraryRelayMap.removeIf(relayInfo -> relayInfo.equals(entry));
+        }
     }
 
 
diff --git a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataRenderManager.java b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataRenderManager.java
index 2844cef8..c1693118 100644
--- a/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataRenderManager.java
+++ b/src/main/java/org/qortal/controller/arbitrary/ArbitraryDataRenderManager.java
@@ -56,7 +56,9 @@ public class ArbitraryDataRenderManager extends Thread {
             return;
         }
         final long minimumTimestamp = now - AUTHORIZATION_TIMEOUT;
-        this.authorizedResources.entrySet().removeIf(entry -> entry.getValue() == null || entry.getValue() < minimumTimestamp);
+        synchronized (this.authorizedResources) {
+            this.authorizedResources.entrySet().removeIf(entry -> entry.getValue() == null || entry.getValue() < minimumTimestamp);
+        }
     }
 
     public boolean isAuthorized(ArbitraryDataResource resource) {
diff --git a/src/main/java/org/qortal/controller/arbitrary/ArbitraryMetadataManager.java b/src/main/java/org/qortal/controller/arbitrary/ArbitraryMetadataManager.java
index fb75ea05..892529fa 100644
--- a/src/main/java/org/qortal/controller/arbitrary/ArbitraryMetadataManager.java
+++ b/src/main/java/org/qortal/controller/arbitrary/ArbitraryMetadataManager.java
@@ -73,7 +73,9 @@ public class ArbitraryMetadataManager {
             return;
         }
         final long requestMinimumTimestamp = now - ArbitraryDataManager.ARBITRARY_REQUEST_TIMEOUT;
-        arbitraryMetadataRequests.entrySet().removeIf(entry -> entry.getValue().getC() == null || entry.getValue().getC() < requestMinimumTimestamp);
+        synchronized (arbitraryMetadataRequests) {
+            arbitraryMetadataRequests.entrySet().removeIf(entry -> entry.getValue().getC() == null || entry.getValue().getC() < requestMinimumTimestamp);
+        }
     }