Speaking from my personal experience, the deployment process gives you the option of installing the client either from network or local location versus downloading from the ESET repository. In the screenshot I have attached, you can see the section that says URL lets you to point to a local network location (either on your local ESET server or any random network share) or you can just choose to pull the file from the official ESET repository.
I am getting the same error. Screenshots attached. It is completely random for me and does not occur on all machines. Happens from time to time and goes away so I don't think it is a problem with the local machines themselves. This was tested with both firewalls on and off so I'm not sure if that's the culprit. Endpoint on the local machines also look perfectly fine