The situation is resolved with sys-fs/zfs-kmod-2.1.10-r1 which includes the required patch to circumvent the issue. I open a Gentoo to keep a trace of it in case of some Gentoo users might still use the problematic version and search around for a Gentoo already known bug. sys-fs/zfs-kmod-2.10 (again not the -r1 revision) is hit by a random data corruption issue as documented in the upstream bug attached to this one. The problematic package version has been masked and removed from the portage tree since a couple of hours. Just upgrade to =sys-fs/zfs-kmod-2.1.10-r1. Nothing more with this bug.