Hi
There was no obvious flicker of the fades noted in the VP preview.
However when exported at a Variable frame rate, flicker was present particularly with the first fade in.
It suggests that the Export frame rate you set may been a variable frame rate and a bit low (30fps?) Do another export and choose a higher Constant frame rate which you may find much smoother.
Your project exported OK at a Constant 30fps here but also smooth with Constant 60fps.
If you consider your first fade in. It's 2.6 seconds. At 30 fps that means around 70 shade increments. These would be regular increments at a constant frame rate and would be barely noticed. If the frame rate varies then the shading increments would
Not necessarily be regular in frequency.
And more importantly, show jumps in the degree of shading to match the changing frame rate....i.e. There would be a discernible flicker.
At a higher Variable frame rate the flicker MAY go unnoticed
Nat