diff --git a/VERSION b/VERSION
index 080c74d0..d0203937 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1!10.5.0
+1!10.5.1
diff --git a/pycloudlib/lxd/instance.py b/pycloudlib/lxd/instance.py
index 45aa0ed3..cf2df7b2 100644
--- a/pycloudlib/lxd/instance.py
+++ b/pycloudlib/lxd/instance.py
@@ -254,7 +254,9 @@ def delete(self, wait=True) -> List[Exception]:
         self._log.debug("deleting %s", self.name)
 
         try:
-            subp(["lxc", "delete", self.name, "--force"])
+            instrument_unmount_failure(
+                subp(["lxc", "delete", self.name, "--force"], rcs=[0, 1])
+            )
         except RuntimeError as e:
             if "Instance not found" not in str(e):
                 return [e]
@@ -367,7 +369,7 @@ def _do_restart(self, force=False, **kwargs):
         cmd = ["lxc", "restart", self.name]
         if force:
             cmd.append("--force")
-        subp(cmd)
+        instrument_unmount_failure(subp(cmd, rcs=[0, 1]))
 
     def restore(self, snapshot_name):
         """Restore instance from a specific snapshot.
@@ -561,3 +563,26 @@ def _wait_for_instance_start(self):
             super()._wait_for_instance_start()
         else:
             self.wait_for_state(desired_state="RUNNING", num_retries=200)
+
+
+def instrument_unmount_failure(result):
+    """Temporary instrumentation.
+
+    introduced to aid debugging ephemeral failures in which lxd fails to
+    unmount during instance deletion - currently checks for open files, if
+    insufficient, further checks of the busy mountpoint may be required
+    """
+    if result.return_code:
+        mount = re.findall(
+            "Failed unmounting instance: Failed to unmount",
+            result.stderr,
+        )
+        if mount:
+            files = subp(["lsof", "+f", "--", mount[0]])
+        else:
+            files = "failure parsing lxd mount error"
+
+        raise RuntimeError(
+            "Failure (rc=%s): %s, open files: [%s]"
+            % (result.return_code, result.stderr, files)
+        )
diff --git a/pycloudlib/result.py b/pycloudlib/result.py
index 9bbc511c..60e3d299 100644
--- a/pycloudlib/result.py
+++ b/pycloudlib/result.py
@@ -24,6 +24,11 @@ def __bool__(self):
         """Boolean behavior."""
         return self.ok
 
+    def __str__(self):
+        return "rc: '{}'\nstdout: '{}'\nstderr: '{}'".format(
+            self.return_code, self.return_code, self.stderr
+        )
+
     @property
     def failed(self):
         """Return boolean if result was failure."""
diff --git a/tests/unit_tests/lxd/test_instance.py b/tests/unit_tests/lxd/test_instance.py
index 0583e712..7ec6597b 100644
--- a/tests/unit_tests/lxd/test_instance.py
+++ b/tests/unit_tests/lxd/test_instance.py
@@ -648,6 +648,7 @@ class TestRestart:
     @mock.patch("pycloudlib.lxd.instance.subp")
     def test_restart_calls_lxc_cmd_with_force_param(self, m_subp, force):
         """Honor force param on restart."""
+        m_subp.return_value = Result("", "", 0)
         instance = LXDInstance(name="my_vm")
         instance._do_restart(force=force)  # pylint: disable=protected-access
         if force:
@@ -657,8 +658,9 @@ def test_restart_calls_lxc_cmd_with_force_param(self, m_subp, force):
 
     @mock.patch("pycloudlib.lxd.instance.LXDInstance.shutdown")
     @mock.patch("pycloudlib.lxd.instance.subp")
-    def test_restart_does_not_shutdown(self, _m_subp, m_shutdown):
+    def test_restart_does_not_shutdown(self, m_subp, m_shutdown):
         """Don't shutdown (stop) instance on restart."""
+        m_subp.return_value = Result("", "", 0)
         instance = LXDInstance(name="my_vm")
         instance._do_restart()  # pylint: disable=protected-access
         assert not m_shutdown.called
@@ -866,6 +868,7 @@ def test_delete_on_ephemeral_instance_calls_shutdown(self, m_subp, m_shutdown, i
 
         Also verify is delete is actually called if instance is not ephemeral.
         """
+        m_subp.return_value = Result("", "", 0)
         instance = LXDInstance(name="test")
 
         with mock.patch.object(type(instance), "ephemeral", is_ephemeral):