openvpn client stopped working with 6.5.0 update

My Turris Omnia just got auto-updated from 6.4.4 to 6.5.0. The openvpn client configuration that I have for multiple years suddenly stopped working properly. The vpn connection shows as connected, but no traffic flows through the router anymore with the vpn on. I have to disable the vpn to get connectivity again.

Which logs can help debug this situation?