could be a mesa bug which is fixed in 18.1.7/18.2.0-rc5+, please test the latter from
ppa:canonical-x/x-staging
which has 18.2.0
could be a mesa bug which is fixed in 18.1.7/18.2.0-rc5+, please test the latter from
ppa:canonical- x/x-staging
which has 18.2.0