Solved this problem by blocking update servers. Here is the solution:
Code
echo "127.0.0.1 update.libreelec.tv" >> /storage/.config/hosts.conf
echo "127.0.0.1 releases.libreelec.tv" >> /storage/.config/hosts.conf
systemctl restart network
Tried a lot of things. LE 12.2.1 installed on Mini M8S PRO with S912 / 16 rom / 2 ram / RJ45: 1000M. Aside from this annoying bug the system is super stable for 1080p@60. Making it my main from now on.