Cluster node appears offline after upgrade to 3.15

lxd-node3:
| id | name | description | address | schema | api_extensions | heartbeat | pending |
±—±------±------------±-----------------±-------±---------------±------------------------------------±--------+
| 3 | lxd-node3 | | 192.168.1.3:8443 | 14 | 138 | 2019-07-18T08:48:29.627169572+02:00 | 0 |
| 4 | lxd-node2 | | 192.168.1.2:8443 | 14 | 138 | 2019-07-18T08:48:29.627000301+02:00 | 0 |
| 5 | lxd-node1 | | 192.168.1.1:8443 | 14 | 138 | 2019-07-18T01:38:30.60775629+02:00 | 0 |
±—±------±------------±-------------------±-------±---------------±------------------------------------±--------+

±—±-----------------+
| id | address |
±—±-----------------+
| 3 | 192.168.1.3:8443 |
| 5 | 192.168.1.2:8443 |
| 6 | 192.168.1.1:8443 |
±—±-----------------+

lxd-node2:
| id | name | description | address | schema | api_extensions | heartbeat | pending |
±—±------±------------±-------------------±-------±---------------±------------------------------------±--------+
| 3 | lxd-node3 | | 192.168.1.3:8443 | 14 | 138 | 2019-07-18T08:49:44.337588653+02:00 | 0 |
| 4 | lxd-node2 | | 192.168.1.2:8443 | 14 | 138 | 2019-07-18T08:49:44.337891201+02:00 | 0 |
| 5 | lxd-node1 | | 192.168.1.1:8443 | 14 | 138 | 2019-07-18T01:38:30.60775629+02:00 | 0 |
±—±------±------------±-----------------±-------±---------------±------------------------------------±--------+

±—±-----------------+
| id | address |
±—±-----------------+
| 3 | 192.168.1.3:8443 |
| 5 | 192.168.1.2:8443 |
| 6 | 192.168.1.1:8443 |
±—±-----------------+

lxd-node1:
| id | name | description | address | schema | api_extensions | heartbeat | pending |
±—±------±------------±-------------------±-------±---------------±------------------------------------±--------+
| 3 | lxd-node3 | | 192.168.1.3:8443 | 14 | 138 | 2019-07-18T08:51:58.090593895+02:00 | 0 |
| 4 | lxd-node2 | | 192.168.1.2:8443 | 14 | 138 | 2019-07-18T08:51:58.090794261+02:00 | 0 |
| 5 | lxd-node1 | | 192.168.1.1:8443 | 14 | 138 | 2019-07-18T01:38:30.60775629+02:00 | 0 |
±—±------±------------±-------------------±-------±---------------±------------------------------------±--------+

±—±-------------------+
| id | address |
±—±-------------------+
| 3 | 192.168.1.3:8443 |
| 5 | 192.168.1.2:8443 |
| 6 | 192.168.1.1:8443 |