Sorry I can't be much help but I just tried this on one of my rpi4's running Ubuntu 20.0.4LTS and it all seemed fine. Seems like further troubleshooting is required. I'm happy to help compare and contrast settings if needed.
==> Log data will now stream in as it occurs:
2020-07-12T04:20:15.598Z [DEBUG] agent: Using random ID as node ID: id=115254c1-bab8-39b7-b559-f87d46b91ff4
2020-07-12T04:20:15.633Z [INFO] agent.server.raft: initial configuration: index=1 servers="[{Suffrage:Voter ID:115254c1-bab8-39b7-b559-f87d46b91ff4 Address:127.0.0.1:8300}]"
2020-07-12T04:20:15.633Z [INFO] agent.server.raft: entering follower state: follower="Node at
127.0.0.1:8300 [Follower]" leader=
2020-07-12T04:20:15.638Z [INFO] agent.server.serf.wan: serf: EventMemberJoin: a895abf23fc3.dc1 127.0.0.1
2020-07-12T04:20:15.642Z [INFO] agent.server.serf.lan: serf: EventMemberJoin: a895abf23fc3 127.0.0.1
2020-07-12T04:20:15.643Z [INFO] agent.server: Adding LAN server: server="a895abf23fc3 (Addr: tcp/
127.0.0.1:8300) (DC: dc1)"
2020-07-12T04:20:15.643Z [INFO] agent.server: Handled event for server in area: event=member-join server=a895abf23fc3.dc1 area=wan
2020-07-12T04:20:15.650Z [INFO] agent: Started DNS server: address=
0.0.0.0:8600 network=tcp
2020-07-12T04:20:15.650Z [INFO] agent: Started DNS server: address=
0.0.0.0:8600 network=udp
2020-07-12T04:20:15.653Z [INFO] agent: Started HTTP server: address=[::]:8500 network=tcp
2020-07-12T04:20:15.655Z [INFO] agent: Started gRPC server: address=[::]:8502 network=tcp
2020-07-12T04:20:15.656Z [INFO] agent: started state syncer
==> Consul agent running!
2020-07-12T04:20:15.690Z [WARN] agent.server.raft: heartbeat timeout reached, starting election: last-leader=
2020-07-12T04:20:15.690Z [INFO] agent.server.raft: entering candidate state: node="Node at
127.0.0.1:8300 [Candidate]" term=2
2020-07-12T04:20:15.691Z [DEBUG] agent.server.raft: votes: needed=1
2020-07-12T04:20:15.691Z [DEBUG] agent.server.raft: vote granted: from=115254c1-bab8-39b7-b559-f87d46b91ff4 term=2 tally=1
2020-07-12T04:20:15.691Z [INFO] agent.server.raft: election won: tally=1
2020-07-12T04:20:15.691Z [INFO] agent.server.raft: entering leader state: leader="Node at
127.0.0.1:8300 [Leader]"
2020-07-12T04:20:15.692Z [INFO] agent.server: cluster leadership acquired
2020-07-12T04:20:15.695Z [DEBUG] agent.server: Cannot upgrade to new ACLs: leaderMode=0 mode=0 found=true leader=
127.0.0.1:8300 2020-07-12T04:20:15.695Z [INFO] agent.server: New leader elected: payload=a895abf23fc3
2020-07-12T04:20:15.701Z [DEBUG] connect.ca.consul: consul CA provider configured: id=07:80:c8:de:f6:41:86:29:8f:9c:b8:17:d6:48:c2:d5:c5:5c:7f:0c:03:f7:cf:97:5a:a7:c1:68:aa:23:ae:81 is_primary=true
2020-07-12T04:20:15.767Z [INFO] agent.server.connect: initialized primary datacenter CA with provider: provider=consul
2020-07-12T04:20:15.767Z [INFO] agent.leader: started routine: routine="federation state anti-entropy"
2020-07-12T04:20:15.767Z [INFO] agent.leader: started routine: routine="federation state pruning"
2020-07-12T04:20:15.767Z [INFO] agent.leader: started routine: routine="CA root pruning"
2020-07-12T04:20:15.767Z [DEBUG] agent.server: Skipping self join check for node since the cluster is too small: node=a895abf23fc3
2020-07-12T04:20:15.769Z [INFO] agent.server: federation state anti-entropy synced
2020-07-12T04:20:15.770Z [INFO] agent.server: member joined, marking health alive: member=a895abf23fc3
2020-07-12T04:20:15.910Z [DEBUG] agent: Skipping remote check since it is managed automatically: check=serfHealth
2020-07-12T04:20:15.912Z [INFO] agent: Synced node info
2020-07-12T04:20:15.912Z [DEBUG] agent: Node info in sync
2020-07-12T04:20:17.736Z [DEBUG] agent: Skipping remote check since it is managed automatically: check=serfHealth
2020-07-12T04:20:17.737Z [DEBUG] agent: Node info in sync
^C
2020-07-12T04:20:32.605Z [INFO] agent: Caught: signal=interrupt
2020-07-12T04:20:32.605Z [INFO] agent: Graceful shutdown disabled. Exiting
2020-07-12T04:20:32.605Z [INFO] agent: Requesting shutdown
2020-07-12T04:20:32.605Z [INFO] agent.server: shutting down server
2020-07-12T04:20:32.605Z [DEBUG] agent.leader: stopping routine: routine="federation state anti-entropy"
2020-07-12T04:20:32.605Z [DEBUG] agent.leader: stopping routine: routine="federation state pruning"
2020-07-12T04:20:32.605Z [DEBUG] agent.leader: stopping routine: routine="CA root pruning"
2020-07-12T04:20:32.606Z [WARN] agent.server.serf.lan: serf: Shutdown without a Leave
2020-07-12T04:20:32.606Z [WARN] agent.server.serf.wan: serf: Shutdown without a Leave
2020-07-12T04:20:32.606Z [INFO] agent.server.router.manager: shutting down
2020-07-12T04:20:32.607Z [INFO] agent: consul server down
2020-07-12T04:20:32.607Z [INFO] agent: shutdown complete
2020-07-12T04:20:32.607Z [INFO] agent: Stopping server: protocol=DNS address=
0.0.0.0:8600 network=tcp
2020-07-12T04:20:32.607Z [INFO] agent: Stopping server: protocol=DNS address=
0.0.0.0:8600 network=udp
2020-07-12T04:20:32.608Z [INFO] agent: Stopping server: protocol=HTTP address=[::]:8500 network=tcp
2020-07-12T04:20:32.608Z [INFO] agent: Waiting for endpoints to shut down
2020-07-12T04:20:32.608Z [INFO] agent: Endpoints down
2020-07-12T04:20:32.608Z [INFO] agent: Exit code: code=1
$ uname -a
Linux enceladus 5.4.0-1013-raspi #13-Ubuntu SMP Mon Jun 15 03:17:37 UTC 2020 aarch64 aarch64 aarch64 GNU/Linux
$ dpkg --print-architecture
arm64