bug btrfs lockup, wayland lipstick or whatever crashed during email sync, connman probably involved

There isn't much info in your report, so hard to say what brought the phone down (and the journal isn't particularly helpful on jolla, at least not to me). If you suspect btrfs, the only viable fix may be a kernel upgrade (unless we expect jolla to backport current btrfs to a 2-years old kernel). See also https://together.jolla.com/question/43043/updated-system-components-kernel-systemd-connman/