IPv6 routes left untouched on IPv4-only VPN connect
When connecting to IPv4 only VPN, openconnect sets IPv4 routes and doesn't change IPv6 routes. If one connects then to a host that is accessible using both IPv4 and IPv6 (has working A and AAAA records), the connection might be established using IPv6 while the expectation is to use VPN.
For reference: cisco anyconnect just clears whole IPv6 routing table on connect and restores on disconnect.