diff --git a/lib/ldclient-rb/impl/data_system/fdv2.rb b/lib/ldclient-rb/impl/data_system/fdv2.rb
index 860b0238..330b8e66 100644
--- a/lib/ldclient-rb/impl/data_system/fdv2.rb
+++ b/lib/ldclient-rb/impl/data_system/fdv2.rb
@@ -129,7 +129,7 @@ def start
           # Start the main coordination thread
           main_thread = Thread.new { run_main_loop }
           main_thread.name = "FDv2-main"
-          @threads << main_thread
+          @lock.synchronize { @threads << main_thread }
 
           @ready_event
         end
@@ -148,12 +148,19 @@ def stop
             end
           end
 
-          # Wait for all threads to complete
-          @threads.each do |thread|
-            next unless thread.alive?
+          # Wait for all threads to complete, including any started while we were joining
+          joined = []
+          loop do
+            pending = @lock.synchronize { @threads.dup } - joined
+            break if pending.empty?
 
-            thread.join(5.0) # 5 second timeout
-            @logger.warn { "[LDClient] Thread #{thread.name} did not terminate in time" } if thread.alive?
+            pending.each do |thread|
+              joined << thread
+              next unless thread.alive?
+
+              thread.join(5.0) # 5 second timeout
+              @logger.warn { "[LDClient] Thread #{thread.name} did not terminate in time" } if thread.alive?
+            end
           end
 
           # Close the store
@@ -333,7 +340,7 @@ def run_synchronizers
           # Start synchronizer loop in a separate thread
           sync_thread = Thread.new { synchronizer_loop }
           sync_thread.name = "FDv2-synchronizers"
-          @threads << sync_thread
+          @lock.synchronize { @threads << sync_thread }
         end
 
         #
@@ -470,8 +477,8 @@ def consume_synchronizer_results(synchronizer, check_recovery: false)
 
               # Set ready event on valid update
               if update.state == LaunchDarkly::Interfaces::DataSource::Status::VALID
-                @ready_event.set
                 record_environment_id(update.environment_id)
+                @ready_event.set
               end
 
               # Update status
diff --git a/spec/impl/data_system/fdv2_datasystem_spec.rb b/spec/impl/data_system/fdv2_datasystem_spec.rb
index eb724467..15ba84cc 100644
--- a/spec/impl/data_system/fdv2_datasystem_spec.rb
+++ b/spec/impl/data_system/fdv2_datasystem_spec.rb
@@ -235,14 +235,12 @@ def with_data_system(initializers, synchronizers)
               .build
 
             changed = Concurrent::Event.new
-            changes = []
-            count = 0
+            changes = Concurrent::Array.new
 
             listener = Object.new
             listener.define_singleton_method(:update) do |flag_change|
-              count += 1
               changes << flag_change
-              changed.set if count == 2
+              changed.set if changes.length >= 2
             end
 
             fdv2 = FDv2.new(sdk_key, config, data_system_config)
@@ -254,9 +252,7 @@ def with_data_system(initializers, synchronizers)
             td.update(td.flag("flagkey").on(false))
             expect(changed.wait(2)).to be true
 
-            expect(changes.length).to eq(2)
-            expect(changes[0].key).to eq("flagkey")
-            expect(changes[1].key).to eq("flagkey")
+            expect(changes.map(&:key).uniq).to eq(["flagkey"])
 
             fdv2.stop
           end
@@ -441,12 +437,12 @@ def with_data_system(initializers, synchronizers)
               .build
 
             changed = Concurrent::Event.new
-            changes = []
+            flag_keys = Concurrent::Array.new
 
             listener = Object.new
             listener.define_singleton_method(:update) do |flag_change|
-              changes << flag_change
-              changed.set if changes.length >= 2
+              flag_keys << flag_change.key
+              changed.set if flag_keys.include?("initialflag") && flag_keys.include?("fdv1replacementflag")
             end
 
             fdv2 = FDv2.new(sdk_key, config, data_system_config)
@@ -454,12 +450,7 @@ def with_data_system(initializers, synchronizers)
 
             ready_event = fdv2.start
             expect(ready_event.wait(2)).to be true
-            expect(changed.wait(3)).to be true
-
-            # Verify we got changes for both flags
-            flag_keys = changes.map { |change| change.key }
-            expect(flag_keys).to include("initialflag")
-            expect(flag_keys).to include("fdv1replacementflag")
+            expect(changed.wait(3)).to be(true), "expected changes for both flags, got #{flag_keys.to_a}"
 
             fdv2.stop
           end