Description of problem:
A redeploy on my 16.2 env was failing due to a restarting horizon container.
Compose: RHOS-16.2-RHEL-8-20210303.n.0

[root@controller-2 stdouts]# podman run -it --rm --net=host undercloud-0.ctlplane.redhat.local:8787/rh-osbs/rhosp16-openstack-horizon:16.2_20210302.1 sh -c 'rpm -qa |grep django'
python3-django-pyscss-2.0.2-17.el8ost.1.noarch
python3-django-appconf-1.0.1-11.el8ost.1.noarch
python3-django20-2.0.13-11.el8ost.2.noarch
python3-django-horizon-16.2.1-2.20210202224949.f6ef2e4.el8ost.1.noarch
python3-django-debreach-1.5.2-6.el8ost.1.noarch
python3-django-compressor-2.2-9.el8ost.1.noarch

The problem is the same as https://bugzilla.redhat.com/show_bug.cgi?id=1919306 which is for 16.1. To fix it we need python-django20-2.0.13-12.el8ost (we have -11).The horizon container is stuck restarting with:
2021-03-10T09:32:29.222395242+00:00 stderr F ++ /usr/bin/python3 /usr/bin/manage.py compress --force
2021-03-10T09:32:30.452515783+00:00 stderr F WARNING:root:"dashboards" and "default_dashboard" in (local_)settings is DEPRECATED now and may be unsupported in some future release. The preferred way to specify the order of dashboards and the default dashboard is the pluggable dashboard mechanism (in /usr/lib/python3.6/site-packages/openstack_dashboard/enabled, /usr/lib/python3.6/site-packages/openstack_dashboard/local/enabled).
2021-03-10T09:32:31.048091084+00:00 stderr F ERROR:scss.ast:Function not found: twbs-font-path:1
2021-03-10T09:32:37.044488791+00:00 stderr F ERROR:scss.compiler:Mixin not found: dropdown-arrow:0 (themes/rcue/bootstrap/components/_dropdowns.scss:61 (themes/rcue/bootstrap/components/_dropdowns.scss:42))
2021-03-10T09:32:37.591328449+00:00 stdout F Found 'compress' tags in:
2021-03-10T09:32:37.591328449+00:00 stdout F 	/usr/lib/python3.6/site-packages/openstack_dashboard/templates/_stylesheets.html
2021-03-10T09:32:37.591328449+00:00 stdout F 	/usr/lib/python3.6/site-packages/openstack_dashboard/templates/serial_console.html
2021-03-10T09:32:37.591328449+00:00 stdout F 	/usr/lib/python3.6/site-packages/openstack_dashboard/templates/horizon/_scripts.html
2021-03-10T09:32:37.591328449+00:00 stdout F 	/usr/lib/python3.6/site-packages/openstack_dashboard/templates/horizon/_conf.html
2021-03-10T09:32:37.591328449+00:00 stdout P Compressing...
2021-03-10T09:32:37.595655068+00:00 stderr F Traceback (most recent call last):
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/django/template/base.py", line 910, in render_annotated
2021-03-10T09:32:37.595655068+00:00 stderr F     return self.render(context)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/django/templatetags/cache.py", line 45, in render
2021-03-10T09:32:37.595655068+00:00 stderr F     value = fragment_cache.get(cache_key)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/django/core/cache/backends/memcached.py", line 77, in get
2021-03-10T09:32:37.595655068+00:00 stderr F     return self._cache.get(key, default)
2021-03-10T09:32:37.595655068+00:00 stderr F TypeError: get() takes 2 positional arguments but 3 were given
2021-03-10T09:32:37.595655068+00:00 stderr F
2021-03-10T09:32:37.595655068+00:00 stderr F During handling of the above exception, another exception occurred:
2021-03-10T09:32:37.595655068+00:00 stderr F
2021-03-10T09:32:37.595655068+00:00 stderr F Traceback (most recent call last):
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/bin/manage.py", line 23, in <module>
2021-03-10T09:32:37.595655068+00:00 stderr F     execute_from_command_line(sys.argv)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/django/core/management/__init__.py", line 371, in execute_from_command_line
2021-03-10T09:32:37.595655068+00:00 stderr F     utility.execute()
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/django/core/management/__init__.py", line 365, in execute
2021-03-10T09:32:37.595655068+00:00 stderr F     self.fetch_command(subcommand).run_from_argv(self.argv)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/django/core/management/base.py", line 288, in run_from_argv
2021-03-10T09:32:37.595655068+00:00 stderr F     self.execute(*args, **cmd_options)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/django/core/management/base.py", line 335, in execute
2021-03-10T09:32:37.595655068+00:00 stderr F     output = self.handle(*args, **options)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/compressor/management/commands/compress.py", line 307, in handle
2021-03-10T09:32:37.595655068+00:00 stderr F     self.compress(**opts)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/compressor/management/commands/compress.py", line 242, in compress
2021-03-10T09:32:37.595655068+00:00 stderr F     rendered = parser.render_nodelist(template, context, node)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/compressor/offline/django.py", line 114, in render_nodelist
2021-03-10T09:32:37.595655068+00:00 stderr F     return node.nodelist.render(context)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/django/template/base.py", line 943, in render
2021-03-10T09:32:37.595655068+00:00 stderr F     bit = node.render_annotated(context)
2021-03-10T09:32:37.595655068+00:00 stderr F   File "/usr/lib/python3.6/site-packages/django/template/base.py", line 913, in render_annotated
2021-03-10T09:32:37.595655068+00:00 stderr F     e.template_debug = context.render_context.template.get_exception_info(e, self.token)
2021-03-10T09:32:37.595655068+00:00 stderr F AttributeError: 'NoneType' object has no attribute 'get_exception_info'

This one is to make sure we do not forget to rebuild the container.