The servers connections that I removed were physically connected in the past.
Though I think you're right, the issue could be caused by some of the still-connected devices.
There are additional warnings of the form:
"Failed to set publishingInterval=5000 on subscription ... scanclass details ...
UaServiceFaultException: status=BAD_ServiceUnsupported, message=The server does not support the requested service."
That only happened after attempting to change the scanclass again.
Though it doesn't report which UA servers are causing the issue.