I came across the similar issue as you, see --->
when execute 'heat stack-list' and by investigating the log of Heat api we saw the error message like below "Unexpected error occurred serving API: Timed out waiting
for a reply to message ID 7daf49ca17cd4070bcfa1041890f84ae" ---->
#
2016-06-22 14:14:33.868 15417 DEBUG heat.common.serializers [req-d8ee1b0a-6568-4482-a177-e8b76356d375 - 69a1bf21012b4311b01d3f998ca95934-0c61356e-f17d-4b8d-ac33-64279d0] JSON response : {"explanation": "The server has ei
ther erred or is incapable of performing the requested operation.", "code": 500, "error": {"message": "Timed out waiting for a reply to message ID 39cea53fd8de46b2a8332c32e047df59", "traceback": "Traceback (most recent c
all last):\n File \"/usr/lib/python2.7/site-packages/heat/api/middleware/fault.py\", line 156, in process_request\n return req.get_response(self.application)\n File \"/usr/lib/python2.7/site-packages/webob/request.p
y\", line 1296, in send\n application, catch_exc_info=False)\n File \"/usr/lib/python2.7/site-packages/webob/request.py\", line 1260, in call_application\n app_iter = application(self.environ, start_response)\n F
ile \"/usr/lib/python2.7/site-packages/webob/dec.py\", line 130, in __call__\n resp = self.call_func(req, args, *self.kwargs)\n File \"/usr/lib/python2.7/site-packages/webob/dec.py\", line 195, in call_func\n re
turn self.func(req, args, *kwargs)\n File \"/usr/lib/python2.7/site-packages/heat/common/wsgi.py\", line 390, in __call__\n response = req.get_response(self.application)\n File \"/usr/lib/python2.7/site-packages/w
ebob/request.py\", line 1296, in send\n application, catch_exc_info=False)\n File \"/usr/lib/python2.7/site-packages/webob/request.py\", line 1260, in call_application\n app_iter = application(self.environ, start_
response)\n File \"/usr/lib/python2.7/site-packages/webob/dec.py\", line 130, in __call__\n resp = self.call_func(req, args, *self.kwargs)\n File \"/usr/lib/python2.7/site-packages/webob/dec.py\", line 195, in cal
l_func\n return self.func(req, args, *kwargs)\n File \"/usr/lib/python2.7/site-packages/heat/common/wsgi.py\", line 390, in __call__\n response = req.get_response(self.application)\n File \"/usr/lib/python2.7/s
ite-packages/webob/request.py\", line 1296, in send\n application, catch_exc_info=False)\n File \"/usr/lib/python2.7/site-packages/webob/request.py\", line 1260, in call_application\n app_iter = application(self.e
nviron, start_response)\n File \"/usr/lib/python2.7/site-packages/webob/dec.py\", line 130, in __call__\n resp = self.call_func(req, args, *self.kwargs)\n File \"/usr/lib/python2.7/site-packages/webob/dec.py\", li
ne 195, in call_func\n return self.func(req, args, *kwargs)\n File \"/usr/lib/python2.7/site-packages/osprofiler/web.py\", line 99, in __call__\n return request.get_response(self.application)\n File \"/usr/lib/
python2.7/site-packages/webob/request.py\", line 1296, in send\n application, catch_exc_info=False)\n File \"/usr/lib/python2.7/site-packages/webob/request.py\", line 1260, in call_application\n app_iter = applica
tion(self.environ, start_response)\n File \"/usr/lib/python2.7/site-packages/webob/dec.py\", line 130, in __call__\n resp = self.call_func(req, args, *self.kwargs)\n File \"/usr/lib/python2.7/site-packages/webob/d
ec ... (more)