Once a day a new agent container gets spawned on every node and is stuck in error "websocket: bad handshake"

Our cluster suffered expired certificate issue like described in #26984.
Somehow I managed to fix the problem as described in suggested solutions of ticket, see comment #26984 (comment) and #26984 (comment).
But afterwards I noticed that every day a new container gets started on all my cluster nodes, that fails to communicate with rancher server and stays stuck in this connection problem, adding a new container day-by-day.
I removed all nodes and re-added them to the cluster but the problem still exists.

Created a ticket too, but no response yet: https://github.com/rancher/rancher/issues/30344

I wonder if this is a real problem for any attempt to upgrade rancher in my current setup.
I fear that starting an upgrade might render my whole cluster broken when there’s already a problem for an agent to communicate with the server ?

Any help appreciate !