diff --git a/src/main/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SpotInstanceService.java b/src/main/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SpotInstanceService.java
index 8a31da6..eb1b0ee 100644
--- a/src/main/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SpotInstanceService.java
+++ b/src/main/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SpotInstanceService.java
@@ -34,7 +34,6 @@
 import static com.thoughtworks.gocd.elasticagent.ecs.domain.SpotRequestState.ACTIVE;
 import static com.thoughtworks.gocd.elasticagent.ecs.domain.SpotRequestState.OPEN;
 import static java.lang.String.format;
-import static java.util.Arrays.asList;
 import static java.util.stream.Collectors.*;
 import static org.apache.commons.collections4.CollectionUtils.union;
 import static org.apache.commons.lang3.StringUtils.containsAny;
@@ -46,7 +45,7 @@ public class SpotInstanceService {
     private final ContainerInstanceHelper containerInstanceHelper;
     private final TerminateOperation terminateOperation;
     private final SpotRequestMatcher spotRequestMatcher;
-    private Set<SpotInstanceRequest> untaggedSpotRequests = Collections.synchronizedSet(new HashSet<>());
+    private final Set<SpotInstanceRequest> untaggedSpotRequests = Collections.synchronizedSet(new HashSet<>());
     private static final SpotInstanceService spotInstanceService = new SpotInstanceService();
 
     private SpotInstanceService() {
@@ -150,15 +149,13 @@ public void tagSpotInstances(PluginSettings pluginSettings) {
 
     public void refreshUnTaggedSpotRequests(PluginSettings pluginSettings) {
         synchronized (untaggedSpotRequests) {
-            List<SpotInstanceRequest> allSpotRequestsforCluster = spotInstanceHelper.getAllSpotRequestsForCluster(pluginSettings);
-            List<String> spotRequestIds = allSpotRequestsforCluster.stream().map(SpotInstanceRequest::getSpotInstanceRequestId).collect(toList());
+            List<SpotInstanceRequest> allSpotRequestsForCluster = spotInstanceHelper.getAllSpotRequestsForCluster(pluginSettings);
+            List<String> spotRequestIds = allSpotRequestsForCluster.stream().map(SpotInstanceRequest::getSpotInstanceRequestId).collect(toList());
 
-            LOG.debug("[refresh-spot-requests] All SpotRequests for Cluster: '{}'", spotRequestIds.stream().collect(joining()));
+            LOG.debug("[refresh-spot-requests] All SpotRequests for Cluster: '{}'", String.join("", spotRequestIds));
             LOG.debug("[refresh-spot-requests] All Untagged spot requests: '{}'", untaggedSpotRequestIds(untaggedSpotRequests));
 
-            untaggedSpotRequests.removeIf(request -> {
-                return spotRequestIds.contains(request.getSpotInstanceRequestId());
-            });
+            untaggedSpotRequests.removeIf(request -> spotRequestIds.contains(request.getSpotInstanceRequestId()));
         }
     }
 
@@ -170,7 +167,7 @@ private String untaggedSpotRequestIds(Set<SpotInstanceRequest> untaggedSpotReque
     private List<SpotInstanceRequest> spotRequestsWithoutRegisteredInstances(PluginSettings pluginSettings, Platform platform,
                                                                              List<Instance> allRegisteredSpotInstancesForPlatform) {
         List<String> registeredInstanceIds = allRegisteredSpotInstancesForPlatform.stream()
-                .map(instance -> instance.getInstanceId()).collect(toList());
+                .map(Instance::getInstanceId).collect(toList());
 
         List<SpotInstanceRequest> spotRequests = spotInstanceHelper
                 .getAllOpenOrSpotRequestsWithRunningInstances(pluginSettings, pluginSettings.getClusterName(), platform);
@@ -226,7 +223,7 @@ private String instanceIds(List<Instance> idleInstancesWithoutTag) {
     }
 
     private Predicate<Instance> getIdleInstancePredicate() {
-        return instance -> !instance.getTags().stream().anyMatch(tag -> tag.getKey().equals(LAST_SEEN_IDLE));
+        return instance -> instance.getTags().stream().noneMatch(tag -> tag.getKey().equals(LAST_SEEN_IDLE));
     }
 
     private Map<String, List<SpotInstanceRequest>> groupSpotRequestsByPlatform(List<SpotInstanceRequest> spotInstanceRequests) {
@@ -246,7 +243,7 @@ private void tagSpotRequest(PluginSettings pluginSettings, ElasticAgentProfilePr
             LOG.debug("[create-agent] Tagging open spot request.");
 
             spotInstanceRequest.withTags(new Tag().withKey("platform").withValue(elasticAgentProfileProperties.platform().name()));
-            spotInstanceHelper.tagSpotResources(pluginSettings, asList(spotInstanceRequest.getSpotInstanceRequestId()), elasticAgentProfileProperties.platform());
+            spotInstanceHelper.tagSpotResources(pluginSettings, List.of(spotInstanceRequest.getSpotInstanceRequestId()), elasticAgentProfileProperties.platform());
         } catch (Exception e) {
             LOG.error("[create-agent] There were errors while tagging spot instance request with id: '{}' cancelling the request.",
                     spotInstanceRequest.getSpotInstanceRequestId(), e);
diff --git a/src/main/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SubnetSelector.java b/src/main/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SubnetSelector.java
index edb788e..bfaf215 100644
--- a/src/main/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SubnetSelector.java
+++ b/src/main/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SubnetSelector.java
@@ -49,8 +49,15 @@ public Subnet selectSubnetWithMinimumEC2Instances(PluginSettings pluginSettings,
     private Subnet findSubnetWithMinimumInstances(List<Subnet> subnets, List<Instance> instances) {
         final Map<Subnet, Long> instancePerSubnet = instancePerSubnet(subnets, instances);
 
+        // Can happen if all found instances happen to be from other elastic agent profiles (which may or may not
+        // be sharing a profile with our plugin configuration
+        if (instancePerSubnet.isEmpty()) {
+            return subnets.get(0);
+        }
+
         return subnets.stream()
-                .filter(subnet -> !instancePerSubnet.containsKey(subnet)).findFirst()
+                .filter(subnet -> !instancePerSubnet.containsKey(subnet))
+                .findFirst()
                 .orElse(Collections.min(instancePerSubnet.entrySet(), Comparator.comparingDouble(Map.Entry::getValue)).getKey());
     }
 
@@ -58,7 +65,7 @@ private Map<Subnet, Long> instancePerSubnet(List<Subnet> subnets, List<Instance>
         final Map<String, Subnet> subnetMap = subnets.stream().collect(Collectors.toMap(Subnet::getSubnetId, subnet -> subnet));
 
         return instances.stream()
-                .filter(instance -> subnetMap.keySet().contains(instance.getSubnetId()))
+                .filter(instance -> subnetMap.containsKey(instance.getSubnetId()))
                 .collect(Collectors.groupingBy(subnet -> subnetMap.get(subnet.getSubnetId()), Collectors.counting()));
     }
 
diff --git a/src/test/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SubnetSelectorTest.java b/src/test/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SubnetSelectorTest.java
index f6918f7..5373b42 100644
--- a/src/test/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SubnetSelectorTest.java
+++ b/src/test/java/com/thoughtworks/gocd/elasticagent/ecs/aws/SubnetSelectorTest.java
@@ -89,6 +89,23 @@ void shouldReturnFirstAvailableSubnetIdIfNoContainerInstanceRunning() {
         assertThat(argumentCaptor.getValue().getSubnetIds()).isEqualTo(Arrays.asList("subnet-1"));
     }
 
+    @Test
+    void shouldReturnFirstAvailableSubnetIdIfContainerInstanceRunningInUnrelatedSubnet() {
+        final ArgumentCaptor<DescribeSubnetsRequest> argumentCaptor = ArgumentCaptor.forClass(DescribeSubnetsRequest.class);
+
+        when(pluginSettings.getSubnetIds()).thenReturn(Arrays.asList("subnet-1"));
+        when(ec2Client.describeSubnets(argumentCaptor.capture())).thenReturn(new DescribeSubnetsResult().withSubnets(
+                new Subnet().withSubnetId("subnet-1").withState("available")
+        ));
+
+        Instance instanceInOtherSubnet = new Instance().withSubnetId("some-other-subnet");
+
+        final Subnet subnet = subnetSelector.selectSubnetWithMinimumEC2Instances(pluginSettings, pluginSettings.getSubnetIds(), List.of(instanceInOtherSubnet));
+
+        assertThat(subnet.getSubnetId()).isEqualTo("subnet-1");
+        assertThat(argumentCaptor.getValue().getSubnetIds()).isEqualTo(Arrays.asList("subnet-1"));
+    }
+
     @Test
     void shouldReturnSubnetIdWhichIsHavingMinimumEC2InstanceRunning() {
         final ArgumentCaptor<DescribeSubnetsRequest> argumentCaptor = ArgumentCaptor.forClass(DescribeSubnetsRequest.class);