Portainer: "Unable to find an agent on any manager node"

[derDieDasJojo]

Bug description
I have a Swarm with 3 Nodes running since several months.
But suddenly now, when I call: https://portainer.*.de/#/stacks or /services or /swarm
I get an error:
Statuscode: 500
{"err":"Unable to find an agent on any manager node"}

portainer & docker swarm manager node:

2018/07/03 07:08:24 Response: map[err:Unable to find an agent on any manager node]
2018/07/03 07:08:24 http: proxy error: Invalid Docker response
2018/07/03 07:08:36 Response: map[err:Unable to find an agent on any manager node]
2018/07/03 07:08:36 http: proxy error: Invalid Docker response
2018/07/03 07:22:25 Response: map[err:Unable to find an agent on any manager node]
2018/07/03 07:22:25 http: proxy error: Invalid Docker response
2018/07/03 07:22:30 Response: map[err:Unable to find an agent on any manager node]
2018/07/03 07:22:30 http: proxy error: Invalid Docker response
2018/07/03 07:25:29 Response: map[err:Unable to find an agent on any manager node]
2018/07/03 07:25:29 http: proxy error: Invalid Docker response

logs from portainer-agent:

2018/07/03 07:16:52 http error: Unable to find an agent on any manager node (code=500)
2018/07/03 07:22:25 http error: Unable to find an agent on any manager node (code=500)
2018/07/03 07:22:30 http error: Unable to find an agent on any manager node (code=500)
2018/07/03 07:22:34 http error: Unable to find an agent on any manager node (code=500)
2018/07/03 07:22:40 http error: Unable to find an agent on any manager node (code=500)
2018/07/03 07:23:31 http error: Unable to find an agent on any manager node (code=500)
2018/07/03 07:25:22 http error: Unable to find an agent on any manager node (code=500)
2018/07/03 07:25:29 http error: Unable to find an agent on any manager node (code=500)
2018/07/03 07:25:29 http error: Unable to find an agent on any manager node (code=500)

But docker swarm manager seems to be able to connect to swarm nodes, because:

docker service ls

shows my the services

Any Ideas how to fix that ?

Expected behavior
I would expect to see the stacks, services or nodes of the swarm

Technical details:

• Portainer version: 1.18.1
• Docker version (managed by Portainer): 18.03.0-ce
• Platform (windows/linux): linux
• Command used to start Portainer (docker run -p 9000:9000 portainer/portainer):
• Browser: Firefox

[derDieDasJojo]

it was a reconnecting issue.
the provider had routing problems and afterwards not everything seem to have reconnected correctly.
i restarted portainer and all portainer-agents.
Now it works again