Node cannot be found among active nodes

Hello,
I’ve updated Graylog 5.2.9 to 6.1.1.
I’ve got an error on some api endpoints (so some functionalities doesn’t work):
Node aaa… cannot be found among active nodes.
The configuration points to /etc/graylog/server/node-id. This file exists, is readalbe by the graylog user and contains the same value as the error.
When I curl http://:9000/api it’s also the same node_id.
I don’t understand why it can’t found the node.
(There is no cluster, it’s just one Graylog server)