Quantum
Is SVP changing its interpolation target framerate constantly because of the monitor's minor refresh rate changes between 143.99333-143.99338?
No. SVP use one multiplier. Refresh rate fluctuations +/-0.001 Hz are not impact on it.
6 framedrops every second
It is not normal.
whole video is moved a bit down. Please fix
It is renderer issue. To work good with black bars lightning function a Renderer must feel video resolution changes on-the-fly. Not all renderers can do it. Try to select another renderer in MPDN (sorry, I didn't try it yet, so I haven't certain solution for now).
About your 144 and 150 Hz solutions. I have 144 Hz monitor too. I use 120 Hz mode for 24 and 30 fps video and 100 Hz mode for 25 and 50 fps video. It gives me integer smoothing factor, so it have less visible artifacts.