watcher strategy workload_stabilization cannot print log normally

When I use watcher strategy workload_stabilization,there exists an error:

Traceback (most recent call last):
  File "/usr/lib/python2.7/logging/__init__.py", line 868, in emit
    msg = self.format(record)
  File "/usr/local/lib/python2.7/dist-packages/oslo_log/handlers.py", line 173, in format
    return logging.StreamHandler.format(self, record) + record.reset_color
  File "/usr/lib/python2.7/logging/__init__.py", line 741, in format
    return fmt.format(record)
  File "/usr/local/lib/python2.7/dist-packages/oslo_log/formatters.py", line 517, in format
    return logging.Formatter.format(self, record)
  File "/usr/lib/python2.7/logging/__init__.py", line 465, in format
    record.message = record.getMessage()
  File "/usr/lib/python2.7/logging/__init__.py", line 329, in getMessage
    msg = msg % self.args
TypeError: not all arguments converted during string formatting
Logged from file workload_stabilization.py, line 459

After analyzing the source code, I think the error location is：
https://opendev.org/openstack/watcher/src/branch/stable/rocky/watcher/decision_engine/strategy/strategies/workload_stabilization.py#L445
https://opendev.org/openstack/watcher/src/branch/stable/rocky/watcher/decision_engine/strategy/strategies/workload_stabilization.py#L448