The error does indicate a networking issue which must be somewhere between your client(s) and the update site.
The update sites themselves (update.nai.com) are fine however as I just tested an update successfully from there.
Looks like a possible connection timeout due to a slow link ?
The screenshot shows threat advisory, which uses a different mechanism and TCP/IP ports to general dat updates.
The McAfee Labs Threat Advisory uses port 8801, not port 80.
See McAfee KB articles:
KB73404 - McAfee Labs Threat Advisory dashboard is blank in ePO 4.6.x
KB66797 - Ports needed by ePO 4.x and ePO 5.0 for communication through a firewall
McAfee Knowledge Base is free for all to search from the link here:
Please make sure that all ports from KB66797 are available as designed for example.
Try changing the update site to McAfeeFTP instead of McAfeeHTTP
Also check if, u have specified the proxy settings if any..
Here they won't allow FTP sites.
So we need to get the updates through Http Site only...