The upstream 1.19.4 update we pushed as: http://advisories.mageia.org/MGASA-2017-0366.html introduced a regression in PRIME syncronization.
Upstream released a 1.19.5 that fixes that and a lot of security fixes: CVE-2017-12176 to CVE-2017-12187
Also added a fix for "XShmGetImage: fix censoring" that is described as: "Visually this fixes chromium/firefox window sharing in multiscreen configurations - without this patch most of the windows on 'secondary' screens are black."
This also should fix https://bugs.freedesktop.org/show_bug.cgi?id=101730.