I saw in the logs of the L3 agent that it is crashing pretty often. It happens like:

2020-05-11 23:56:06.947 136139 DEBUG neutron.agent.l3.router_info [-] removing port {'id': 'f64ca38d-dc13-4ce2-8641-9563a297c96e', 'name': '', 'network_id': 'f4aea80e-30cf-4482-91b9-c210e9a919dc', 'tenant_id': 'ff7f213ca16e4663bf2f9c629389b062', 'mac_address': 'fa:16:3e:be:53:e6', 'admin_state_up': True, 'status': 'D
OWN', 'device_id': '69351713-037a-46ca-b4bb-59cdc7c37b1b', 'device_owner': 'network:router_interface_distributed', 'fixed_ips': [{'subnet_id': '803eb270-25a5-4536-9c0f-b515dda3b820', 'ip_address': '2001:db8::1', 'prefixlen': 64}], 'allowed_address_pairs': [], 'extra_dhcp_opts': [], 'security_groups': [], 'description
': '', 'binding:vnic_type': 'normal', 'binding:profile': {}, 'binding:host_id': '', 'binding:vif_type': 'distributed', 'binding:vif_details': {}, 'qos_policy_id': None, 'port_security_enabled': False, 'dns_name': '', 'dns_assignment': [{'ip_address': '2001:db8::1', 'hostname': 'host-2001-db8--1', 'fqdn': 'host-2001-d
b8--1.openstacklocal.'}], 'resource_request': None, 'ip_allocation': 'immediate', 'tags': [], 'created_at': '2020-05-11T23:52:09Z', 'updated_at': '2020-05-11T23:52:20Z', 'revision_number': 7, 'project_id': 'ff7f213ca16e4663bf2f9c629389b062', 'subnets': [{'id': '803eb270-25a5-4536-9c0f-b515dda3b820', 'cidr': '2001:db8
::/64', 'gateway_ip': '2001:db8::1', 'dns_nameservers': [], 'ipv6_ra_mode': 'dhcpv6-stateless', 'subnetpool_id': None}], 'extra_subnets': [{'id': '0c51c948-69b0-4122-9237-a6dda322a0ef', 'cidr': '10.100.0.0/28', 'gateway_ip': '10.100.0.1', 'dns_nameservers': [], 'ipv6_ra_mode': None, 'subnetpool_id': None}], 'address_
scopes': {'4': None, '6': None}, 'mtu': 1450} from internal_ports cache _process_internal_ports /usr/lib/python3.6/site-packages/neutron/agent/l3/router_info.py:621
2020-05-11 23:56:06.948 136139 DEBUG neutron.agent.l3.router_info [-] Spawning radvd daemon in router device: 69351713-037a-46ca-b4bb-59cdc7c37b1b enable_radvd /usr/lib/python3.6/site-packages/neutron/agent/l3/router_info.py:578
2020-05-11 23:56:06.949 136139 DEBUG neutron.agent.linux.utils [-] Running command (rootwrap daemon): ['radvd-kill', '9', '255351'] execute_rootwrap_daemon /usr/lib/python3.6/site-packages/neutron/agent/linux/utils.py:103
2020-05-11 23:56:07.874 137076 DEBUG oslo.privsep.daemon [-] privsep: reply[140114300415016]: (4, True) _call_back /usr/lib/python3.6/site-packages/oslo_privsep/daemon.py:475
2020-05-11 23:56:07.962 137076 DEBUG oslo.privsep.daemon [-] privsep: reply[140114300415016]: (4, None) _call_back /usr/lib/python3.6/site-packages/oslo_privsep/daemon.py:475
2020-05-11 23:56:08.056 136139 DEBUG oslo_concurrency.lockutils [req-2068d0fc-4ef7-4f5b-97eb-3adf30628d45 - - - - -] Acquired lock "singleton_lock" lock /usr/lib/python3.6/site-packages/oslo_concurrency/lockutils.py:265
2020-05-11 23:56:08.056 136139 DEBUG oslo_concurrency.lockutils [req-2068d0fc-4ef7-4f5b-97eb-3adf30628d45 - - - - -] Releasing lock "singleton_lock" lock /usr/lib/python3.6/site-packages/oslo_concurrency/lockutils.py:281
2020-05-11 23:56:08.057 136139 INFO oslo_rootwrap.client [req-2068d0fc-4ef7-4f5b-97eb-3adf30628d45 - - - - -] Stopping rootwrap daemon process with pid=207658
2020-05-11 23:56:08.062 136139 CRITICAL neutron [req-2068d0fc-4ef7-4f5b-97eb-3adf30628d45 - - - - -] Unhandled error: RuntimeError: Second simultaneous read on fileno 16 detected.  Unless you really know what you're doing, make sure that only one greenthread can read any particular socket.  Consider using a pools.Pool. If you do know what you're doing and want to disable this error, call eventlet.debug.hub_prevent_multiple_readers(False) - MY THREAD=<built-in method switch of greenlet.greenlet object at 0x7f6ef135f6d0>; THAT THREAD=FdListener('read', 16, <built-in method switch of greenlet.greenlet object at 0x7f6ee71aa930>, <built-in method throw of greenlet.greenlet object at 0x7f6ee71aa930>)
2020-05-11 23:56:08.062 136139 ERROR neutron Traceback (most recent call last):
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib64/python3.6/weakref.py", line 624, in _exitfunc
2020-05-11 23:56:08.062 136139 ERROR neutron     f()
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib64/python3.6/weakref.py", line 548, in __call__
2020-05-11 23:56:08.062 136139 ERROR neutron     return info.func(*info.args, **(info.kwargs or {}))
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/oslo_rootwrap/client.py", line 103, in _shutdown
2020-05-11 23:56:08.062 136139 ERROR neutron     manager.rootwrap().shutdown()
2020-05-11 23:56:08.062 136139 ERROR neutron   File "<string>", line 2, in shutdown
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib64/python3.6/multiprocessing/managers.py", line 757, in _callmethod
2020-05-11 23:56:08.062 136139 ERROR neutron     kind, result = conn.recv()
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/oslo_rootwrap/jsonrpc.py", line 132, in recv
2020-05-11 23:56:08.062 136139 ERROR neutron     s = self.recv_bytes()
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/oslo_rootwrap/jsonrpc.py", line 121, in recv_bytes
2020-05-11 23:56:08.062 136139 ERROR neutron     l = struct.unpack('!Q', self.recvall(8))[0]
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/oslo_rootwrap/jsonrpc.py", line 148, in _recvall_slow
2020-05-11 23:56:08.062 136139 ERROR neutron     piece = self._socket.recv(remaining)
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/eventlet/greenio/base.py", line 366, in recv
2020-05-11 23:56:08.062 136139 ERROR neutron     return self._recv_loop(self.fd.recv, b'', bufsize, flags)
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/eventlet/greenio/base.py", line 360, in _recv_loop
2020-05-11 23:56:08.062 136139 ERROR neutron     self._read_trampoline()
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/eventlet/greenio/base.py", line 331, in _read_trampoline
2020-05-11 23:56:08.062 136139 ERROR neutron     timeout_exc=socket_timeout('timed out'))
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/eventlet/greenio/base.py", line 210, in _trampoline
2020-05-11 23:56:08.062 136139 ERROR neutron     mark_as_closed=self._mark_as_closed)
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/eventlet/hubs/__init__.py", line 155, in trampoline
2020-05-11 23:56:08.062 136139 ERROR neutron     listener = hub.add(hub.READ, fileno, current.switch, current.throw, mark_as_closed)
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/eventlet/hubs/epolls.py", line 22, in add
2020-05-11 23:56:08.062 136139 ERROR neutron     listener = hub.BaseHub.add(self, evtype, fileno, cb, tb, mac)
2020-05-11 23:56:08.062 136139 ERROR neutron   File "/usr/lib/python3.6/site-packages/eventlet/hubs/hub.py", line 181, in add
2020-05-11 23:56:08.062 136139 ERROR neutron     evtype, fileno, evtype, cb, bucket[fileno]))
2020-05-11 23:56:08.062 136139 ERROR neutron RuntimeError: Second simultaneous read on fileno 16 detected.  Unless you really know what you're doing, make sure that only one greenthread can read any particular socket.  Consider using a pools.Pool. If you do know what you're doing and want to disable this error, call eventlet.debug.hub_prevent_multiple_readers(False) - MY THREAD=<built-in method switch of greenlet.greenlet object at 0x7f6ef135f6d0>; THAT THREAD=FdListener('read', 16, <built-in method switch of greenlet.greenlet object at 0x7f6ee71aa930>, <built-in method throw of greenlet.greenlet object at 0x7f6ee71aa930>)
2020-05-11 23:56:08.062 136139 ERROR neutron
2020-05-11 23:56:12.871 295400 INFO neutron.common.config [-] Logging enabled!
2020-05-11 23:56:12.872 295400 INFO neutron.common.config [-] /usr/bin/neutron-l3-agent version 15.0.3.dev79