Flask app load/stress testing errors

I have a simple Flask application that has about 7 end points (GET). No POST operation is used by any end point. When a specific GET request is received I return a JSON file back after a little bit of computation. I am using locust to load test it. I notice that if I use 100 users in locust and a hatch rate of 20 initially it runs smoothly for a bit and then I start seeing these errors from Flask (below). Is there something I can do to fix such an issue?

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Exception happened during processing of request from ('127.0.0.1', 65360)
Traceback (most recent call last):
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/SocketServer.py", line 596, in process_request_thread
File  "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/SocketServer.py", line 331, in finish_request
File   "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/SocketServer.py", line 652, in __init__
File "/Library/Python/2.7/site-packages/werkzeug/serving.py", line 217, in handle
File   "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/BaseHTTPServer.py", line 340, in handle
File "/Library/Python/2.7/site-packages/werkzeug/serving.py", line 252, in handle_one_request
File "/Library/Python/2.7/site-packages/werkzeug/serving.py", line 200, in run_wsgi
ImportError: No module named debug.tbtools

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