Mullvad VPN through 2024.1 on Android does not set a DNS server in the blocking state (after a hard failure to create a tunnel), and thus DNS traffic can leave the device. Data showing that the affected device was the origin of sensitive DNS requests may be observed and logged by operators of unintended DNS servers.
https://news.ycombinator.com/item?id=40247604
https://mullvad.net/en/blog/dns-traffic-can-leak-outside-the-vpn-tunnel-on-android
https://github.com/mullvad/mullvadvpn-app/tags
https://github.com/mullvad/mullvadvpn-app/commit/0c39306a40f426853d617e20d596942e41091f13
https://github.com/mullvad/mullvadvpn-app/blob/main/CHANGELOG.md