Forza is a known issue which we are investigating. Workaround is to try enabling HBCC found under Radeon Settings > Gaming > Global Settings.
Your other issue could be several things, difficult to say with such little information provided. INFORMATION REQUIRED WHEN POSTING A QUESTION
I have to join this thread, unfortunately... I just got my second Vega 64 Strix ROG from Asus, and ever since I got it I'm experiencing this screen losing signals and system lock ups. Both on 18.3.3 and 18.3.4. Never noticed them while I used this same card for the past 3 months, but did had some other issues. Specs, 1800X, ASRock Fatal1ty Pro Gaming with its latest BIOS, 2x16GB of RAM working at 2666MHz, Seasonic 1000W Prime Gold, using separated 8-pins for each card (4 in total), etc. Linked to a Benq BL3201PT via Display Port.