Node reboot with flannel

i have a problem with Flannel.
I have a cluster with 12 nodes. All is working correctly with flannel as cni plugin.
The pb is when i reboot the node.
Due to timeouts no pods are removed, the node reboot is fast and containers are restarted by docker.
But it containers terminate with errors :

Failed to create pod sandbox: rpc error: code = Unknown desc = failed to set up sandbox container [...] network for pod [...]: networkPlugin cni failed to set up pod [...] network: open /run/flannel/subnet.env: no such file or directory

The file is present on the filesystem. But it take some seconds at boot to be present. I think the pb is here.
If i remove the flannel pod on the node, it is recreated and unlock other containers.

Someone has already have this issue? (not found on search)