diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/assignment/TrainedModelAssignmentClusterService.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/assignment/TrainedModelAssignmentClusterService.java
index 2caf338d2a3c7..ca9a99f2d96f5 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/assignment/TrainedModelAssignmentClusterService.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/assignment/TrainedModelAssignmentClusterService.java
@@ -164,6 +164,8 @@ public void clusterChanged(ClusterChangedEvent event) {
         }
 
         if (eventStateMinTransportVersionIsBeforeDistributedModelAllocationTransportVersion(event)) {
+            logger.trace("min transport version is before assignment change on " + event.state().nodes().getAllNodes().size() + " nodes");
+
             // we should not try to rebalance assignments while there may be nodes running on a version
             // prior to introducing distributed model allocation.
             // But we should remove routing to removed or shutting down nodes.
@@ -238,6 +240,7 @@ public void onFailure(Exception e) {
     }
 
     private void removeRoutingToRemovedOrShuttingDownNodes(ClusterChangedEvent event) {
+        logger.trace("remove routing to removed or shutting down nodes ");
         if (areAssignedNodesRemoved(event)) {
             submitUnbatchedTask("removing routing entries for removed or shutting down nodes", new ClusterStateUpdateTask() {
                 @Override
@@ -282,6 +285,7 @@ static boolean areAssignedNodesRemoved(ClusterChangedEvent event) {
 
     // Visible for testing
     static ClusterState removeRoutingToUnassignableNodes(ClusterState currentState) {
+        logger.trace("remove routing to unassignable nodes");
         Set<String> assignableNodes = getAssignableNodes(currentState).stream().map(DiscoveryNode::getId).collect(Collectors.toSet());
         TrainedModelAssignmentMetadata metadata = TrainedModelAssignmentMetadata.fromState(currentState);
         TrainedModelAssignmentMetadata.Builder builder = TrainedModelAssignmentMetadata.builder(currentState);
@@ -431,6 +435,7 @@ public void createNewModelAssignment(
     }
 
     public void setModelAssignmentToStopping(String modelId, ActionListener<AcknowledgedResponse> listener) {
+        logger.trace("set to stopping");
         submitUnbatchedTask("set model assignment stopping", new ClusterStateUpdateTask() {
             @Override
             public ClusterState execute(ClusterState currentState) {
@@ -450,6 +455,7 @@ public void clusterStateProcessed(ClusterState oldState, ClusterState newState)
     }
 
     public void removeModelAssignment(String deploymentId, ActionListener<AcknowledgedResponse> listener) {
+        logger.trace("remove model assignments");
         submitUnbatchedTask("delete model deployment assignment", new ClusterStateUpdateTask() {
             @Override
             public ClusterState execute(ClusterState currentState) {
@@ -486,6 +492,7 @@ public void clusterStateProcessed(ClusterState oldState, ClusterState newState)
 
     // Used by the reset action directly
     public void removeAllModelAssignments(ActionListener<AcknowledgedResponse> listener) {
+        logger.trace("remove all assignments");
         submitUnbatchedTask("delete all model assignments", new ClusterStateUpdateTask() {
             @Override
             public ClusterState execute(ClusterState currentState) {
@@ -518,9 +525,11 @@ private static ClusterState forceUpdate(ClusterState currentState, TrainedModelA
         logger.debug(() -> format("updated assignments: %s", modelAssignments.build()));
         Metadata.Builder metadata = Metadata.builder(currentState.metadata());
         if (currentState.getMinTransportVersion().onOrAfter(RENAME_ALLOCATION_TO_ASSIGNMENT_TRANSPORT_VERSION)) {
+            logger.trace("putting custom new name");
             metadata.putCustom(TrainedModelAssignmentMetadata.NAME, modelAssignments.build())
                 .removeCustom(TrainedModelAssignmentMetadata.DEPRECATED_NAME);
         } else {
+            logger.trace("putting custom old name");
             metadata.putCustom(TrainedModelAssignmentMetadata.DEPRECATED_NAME, modelAssignments.buildOld());
         }
         return ClusterState.builder(currentState).metadata(metadata).build();
@@ -616,6 +625,7 @@ ClusterState stopPlatformSpecificModelsInHeterogeneousClusters(
                 modelToAdd.get().getModelId(),
                 mlNodesArchitectures
             );
+            logger.info(reasonToStop);
             updatedState = callSetToStopping(reasonToStop, modelToAdd.get().getDeploymentId(), clusterState);
         }
         return updatedState;
diff --git a/x-pack/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/MLModelDeploymentsUpgradeIT.java b/x-pack/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/MLModelDeploymentsUpgradeIT.java
index b9fbf0b6b1f03..87d605d29fa86 100644
--- a/x-pack/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/MLModelDeploymentsUpgradeIT.java
+++ b/x-pack/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/MLModelDeploymentsUpgradeIT.java
@@ -73,7 +73,7 @@ public void setUpLogging() throws IOException {
             {
               "persistent": {
                 "logger.org.elasticsearch.xpack.ml.inference": "TRACE",
-                "logger.org.elasticsearch.xpack.ml.inference.assignments": "DEBUG",
+                "logger.org.elasticsearch.xpack.ml.inference.assignments": "TRACE",
                 "logger.org.elasticsearch.xpack.ml.process": "DEBUG",
                 "logger.org.elasticsearch.xpack.ml.action": "TRACE"
               }
@@ -97,6 +97,7 @@ public void removeLogging() throws IOException {
         client().performRequest(request);
     }
 
+    @AwaitsFix(bugUrl = "mute to try and reproduce https://github.com/elastic/elasticsearch/issues/100379")
     public void testTrainedModelDeployment() throws Exception {
         assumeTrue("NLP model deployments added in 8.0", UPGRADE_FROM_VERSION.onOrAfter(Version.V_8_0_0));