My multi node devstack environment is re-installed in August 8th.
Bug report is under default watcher which means api_version of nova_client is 2.

After changing api_version of nova_client to 2.53, exception has changed:

8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling Traceback (most recent call last):
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/opt/stack/watcher/watcher/decision_engine/sc
heduling.py", line 74, in _sync
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     timed_sync()
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/opt/stack/watcher/watcher/decision_engine/scheduling.py", line 62, in _timed_sync
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     sync_func()
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/opt/stack/watcher/watcher/decision_engine/model/collector/base.py", line 185, in synchronize
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     self.cluster_data_model = self.execute()
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/opt/stack/watcher/watcher/decision_engine/model/collector/nova.py", line 63, in execute
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     return builder.execute()
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/opt/stack/watcher/watcher/decision_engine/model/collector/nova.py", line 368, in execute
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     self._add_physical_layer()
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/opt/stack/watcher/watcher/decision_engine/model/collector/nova.py", line 99, in _add_physical_layer
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     self.add_compute_node(cnode)
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/opt/stack/watcher/watcher/decision_engine/model/collector/nova.py", line 103, in add_compute_node
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     compute_node = self.build_compute_node(node)
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/opt/stack/watcher/watcher/decision_engine/model/collector/nova.py", line 144, in build_compute_node
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     compute_node = element.ComputeNode(**node_attributes)
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/opt/stack/watcher/watcher/decision_engine/model/element/base.py", line 48, in __init__
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     super(Element, self).__init__(context, **kwargs)
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/usr/local/lib/python2.7/dist-packages/oslo_versionedobjects/base.py", line 307, in __init__
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     setattr(self, key, kwargs[key])
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/usr/local/lib/python2.7/dist-packages/oslo_versionedobjects/base.py", line 72, in setter
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     field_value = field.coerce(self, name, value)
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/usr/local/lib/python2.7/dist-packages/oslo_versionedobjects/fields.py", line 195, in coerce
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     return self._type.coerce(obj, attr, value)
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling   File "/usr/local/lib/python2.7/dist-packages/oslo_versionedobjects/fields.py", line 408, in coerce
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling     v = int(value)
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling ValueError: invalid literal for int() with base 10: 'f25db24d-1dd9-4264-a7d3-cc06471ea0be'
 8月 09 22:35:26 w001 watcher-decision-engine[17103]: 2017-08-09 22:35:26.717 TRACE watcher.decision_engine.scheduling