diff --git a/cura/Machines/ContainerTree.py b/cura/Machines/ContainerTree.py
index 5daae32826..6c4a0c3450 100644
--- a/cura/Machines/ContainerTree.py
+++ b/cura/Machines/ContainerTree.py
@@ -146,7 +146,10 @@ class ContainerTree:
         #
         #   The ``JobQueue`` will schedule this on a different thread.
         def run(self) -> None:
-            for stack in self.container_stacks:
+            for stack in self.container_stacks:  # Load all currently-added containers.
+                # Allow a thread switch after every container.
+                # Experimentally, sleep(0) didn't allow switching. sleep(0.1) or sleep(0.2) neither.
+                # We're in no hurry though. Half a second is fine.
                 time.sleep(0.5)
                 if not isinstance(stack, GlobalStack):
                     continue