diff --git a/python/plugins/processing/ProcessingPlugin.py b/python/plugins/processing/ProcessingPlugin.py
index 9c2cd1b8bc1..87fe6e96af6 100644
--- a/python/plugins/processing/ProcessingPlugin.py
+++ b/python/plugins/processing/ProcessingPlugin.py
@@ -253,6 +253,7 @@ class ProcessingPlugin:
         self.resultsDock.setVisible(False)
         self.iface.removeDockWidget(self.resultsDock)
 
+        self.toolbox.deleteLater()
         self.menu.deleteLater()
 
         # delete temporary output files
diff --git a/python/plugins/processing/core/Processing.py b/python/plugins/processing/core/Processing.py
index b546fe4aa7d..06289b325c8 100644
--- a/python/plugins/processing/core/Processing.py
+++ b/python/plugins/processing/core/Processing.py
@@ -85,11 +85,15 @@ class Processing(object):
         if "model" in [p.id() for p in QgsApplication.processingRegistry().providers()]:
             return
         # Add the basic providers
-        for c in QgsProcessingProvider.__subclasses__():
+        for c in [
+            QgisAlgorithmProvider,
+            Grass7AlgorithmProvider,
+            GdalAlgorithmProvider,
+            SagaAlgorithmProvider,
+            ScriptAlgorithmProvider,
+            ModelerAlgorithmProvider
+        ]:
             p = c()
-            if p.id() in ('native', '3d'):
-                # c++ providers are already registered
-                continue
             if QgsApplication.processingRegistry().addProvider(p):
                 Processing.BASIC_PROVIDERS.append(p)
         # And initialize
diff --git a/python/plugins/processing/modeler/ModelerAlgorithmProvider.py b/python/plugins/processing/modeler/ModelerAlgorithmProvider.py
index 5ba5efb77a6..3c9be7a4b1f 100644
--- a/python/plugins/processing/modeler/ModelerAlgorithmProvider.py
+++ b/python/plugins/processing/modeler/ModelerAlgorithmProvider.py
@@ -63,7 +63,10 @@ class ModelerAlgorithmProvider(QgsProcessingProvider):
 
         # must reload models if providers list is changed - previously unavailable algorithms
         # which models depend on may now be available
-        QgsApplication.processingRegistry().providerAdded.connect(self.refreshAlgorithms)
+        QgsApplication.processingRegistry().providerAdded.connect(self.onProviderAdded)
+
+    def onProviderAdded(self, provider_id):
+        self.refreshAlgorithms()
 
     def load(self):
         ProcessingConfig.settingIcons[self.name()] = self.icon()