diff --git a/core/federated/federate.c b/core/federated/federate.c
index af8fcd177..b55644108 100644
--- a/core/federated/federate.c
+++ b/core/federated/federate.c
@@ -622,7 +622,7 @@ static int handle_tagged_message(int* socket, int fed_id) {
 #ifdef FEDERATED_DECENTRALIZED
     // For tardy messages in decentralized coordination, we need to figure out what the actual tag will be.
     // (Centralized coordination errors out with tardy messages).
-    if (lf_tag_compare(intended_tag, env->current_tag) <= 0) {
+    if (lf_tag_compare(intended_tag, env->current_tag) <= 0 && env->execution_started) {
       // Message is tardy.
       actual_tag = env->current_tag;
       actual_tag.microstep++;
diff --git a/core/threaded/scheduler_NP.c b/core/threaded/scheduler_NP.c
index 65f9c542f..b50dd5b69 100644
--- a/core/threaded/scheduler_NP.c
+++ b/core/threaded/scheduler_NP.c
@@ -95,13 +95,17 @@ static inline void _lf_sched_insert_reaction(lf_scheduler_t* scheduler, reaction
  *
  * @return 1 if any reaction is ready. 0 otherwise.
  */
-static int _lf_sched_distribute_ready_reactions(lf_scheduler_t* scheduler) {
+static int _lf_sched_distribute_ready_reactions_locked(lf_scheduler_t* scheduler) {
   // Note: All the threads are idle, which means that they are done inserting
   // reactions. Therefore, the reaction vectors can be accessed without
   // locking a mutex.
   while (scheduler->custom_data->next_reaction_level <= scheduler->max_reaction_level) {
 #ifdef FEDERATED
-    lf_stall_advance_level_federation(scheduler->env, scheduler->custom_data->next_reaction_level);
+    environment_t* top_level_env;
+    _lf_get_environments(&top_level_env);
+    if (scheduler->env == top_level_env) {
+      lf_stall_advance_level_federation_locked(scheduler->custom_data->next_reaction_level);
+    }
 #endif
     scheduler->custom_data->executing_reactions =
         scheduler->custom_data->triggered_reactions[scheduler->custom_data->next_reaction_level];
@@ -163,30 +167,28 @@ static void _lf_sched_signal_stop(lf_scheduler_t* scheduler) {
 static void _lf_scheduler_try_advance_tag_and_distribute(lf_scheduler_t* scheduler) {
   // Reset the index
   environment_t* env = scheduler->env;
+  LF_MUTEX_LOCK(&env->mutex);
   scheduler->indexes[scheduler->custom_data->next_reaction_level - 1] = 0;
-
   // Loop until it's time to stop or work has been distributed
   while (true) {
     if (scheduler->custom_data->next_reaction_level == (scheduler->max_reaction_level + 1)) {
       scheduler->custom_data->next_reaction_level = 0;
-      LF_MUTEX_LOCK(&env->mutex);
       // Nothing more happening at this tag.
       LF_PRINT_DEBUG("Scheduler: Advancing tag.");
       // This worker thread will take charge of advancing tag.
       if (_lf_sched_advance_tag_locked(scheduler)) {
         LF_PRINT_DEBUG("Scheduler: Reached stop tag.");
         _lf_sched_signal_stop(scheduler);
-        LF_MUTEX_UNLOCK(&env->mutex);
         break;
       }
-      LF_MUTEX_UNLOCK(&env->mutex);
     }
 
-    if (_lf_sched_distribute_ready_reactions(scheduler) > 0) {
+    if (_lf_sched_distribute_ready_reactions_locked(scheduler) > 0) {
       _lf_sched_notify_workers(scheduler);
       break;
     }
   }
+  LF_MUTEX_UNLOCK(&env->mutex);
 }
 
 /**