Varnish: How often is DNS name lookup done when specified in ACL

NetBIOS is a different thing to DNS. NetBIOS name resolution uses either broadcasts (limited to a single subnet on an ip network typically), WINS (wider scope, requires a WINS server to be identified generally provided via DHCP), or an LMHOSTS file. If NetBIOS name resolution is failing across a VPN connection but working within your LAN environment and that LAN uses WINS then you should look at the DHCP scope options being provided by your VPN client (these may be configured at the client end or provided dynamically by the VPN gateway).

If you mean the hostname (e.g. the MyPC part of MyPC.somedomain.com) does not resolve across your VPN even though it does when you are in your office then the issue is that your VPN is either not appending the domain suffix that you need or possibly that your VPN is not redirecting DNS.

Without a bit more information it's hard to be more specific - post the output of ipconfig /all when connected via VPN and when connected to the LAN for a start.

Well, example.local is typically an mDNS (Zeroconf) address, so there's every possibility that your mDNS config has broken in some way, and it's taking a few seconds for that to timeout before it falls back to /etc/hosts.

Why not just add localhost as a ServerAlias and just access it via that name? Otherwise, at least use a domain that doesn't have a top-level domain that has a different meaning to your system.