I have been able to reproduce this issue under a recently upgraded Pulp to 2.8.2.
It is not directly debuggable, as of https://pulp.plan.io/issues/1485, but I have been able to extract the following stacktrace out of strace-ing apache's mod_wsgi process.
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) Internal Server Error: /v3/modules/puppetlabs-apt\0", 96, 0, NULL, 0) = 96
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) Traceback (most recent call last):\0", 81, 0, NULL, 0) = 81
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) File \"/usr/lib/python2.6/site-packages/django/core/handlers/base.py\", line 148, in get_response\0", 144, 0, NULL, 0) = 144
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) response = callback(request, **param_dict)\0", 93, 0, NULL, 0) = 93
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) File \"/usr/lib/python2.6/site-packages/django/utils/decorators.py\", line 91, in _wrapped_view\0", 142, 0, NULL, 0) = 142
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) response = view_func(request, *args, **kwargs)\0", 97, 0, NULL, 0) = 97
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) File \"/usr/lib/python2.6/site-packages/django/views/defaults.py\", line 20, in page_not_found\0", 141, 0, NULL, 0) = 141
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) t = loader.get_template(template_name) # You need to create a 404.html template.\0", 131, 0, NULL, 0) = 131
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) File \"/usr/lib/python2.6/site-packages/django/template/loader.py\", line 145, in get_template\0", 141, 0, NULL, 0) = 141
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) template, origin = find_template(template_name)\0", 98, 0, NULL, 0) = 98
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) File \"/usr/lib/python2.6/site-packages/django/template/loader.py\", line 138, in find_template\0", 142, 0, NULL, 0) = 142
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) raise TemplateDoesNotExist(name)\0", 83, 0, NULL, 0) = 83
[pid 32546] sendto(14, "<27>pulp: django.request:ERROR: (32423-67584) TemplateDoesNotExist: 404.html\0", 77, 0, NULL, 0) = 77
Upon a request to the `/v3/modules/puppetlabs-apt` (currently missing) endpoint.
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