Hi @Lightsword,
A direct update from 3.8.12 to 3.8.15-12 is not recommended and the errors you reported are expected. Try a new install of 3.8.15 followed by importing your data back. Or you could also use yum to downgrade to 3.8.15-10, make sure everything works properly and then upgrade to the latest. That should work.
Your OS and boot errors on the other hand, are not Rockstor related so I can’t provide and expertise there. Sorry.