Same thing happening here:
I had a 5 second loop which wasn't flickering until I doubled the length of the first blocks to 2 seconds, then the flickering started. Every block is full white except for red bands so there is nothing in the loop to cause the flickering.
The flicker occurs when it hits the beginning of the loop, but doesn't happen every time. Seems to work properly at random.
Gear: AMD Ryzen 9 3950x, Gigabyte Aorus Xtreme mobo, 128GB 3600 corsair vengeance pro DDR4, Radeon Vega 64 8GB, Sabrent Rocket M.2.
Thanks!