I am having this exact same issue with Resolve 15. As soon as I add a single color grading effect – doesn’t matter which one, LUT, curve…etc., the video flickers between the original ungraded clip and the graded clip – both in the timeline and in all final renders. Did you ever figure out a permanent fix for this? It happens on both my laptop and my main computer.
Computer Specs: AMD FX-9590 Vishera 8-Core 4.7GHz Processor | SAPPHIRE TRI-X OC Radeon R9 290X 4GB 512-Bit GDDR5 Video Card | G.SKILL Trident X Series 1866 16GB DDR3 RAM | CORSAIR Hydro H105 Liquid CPU Cooler