You don't need these lines.
LoadPlugin("C:\Program Files (x86)\AviSynth+\plugins64+\ffms2.dll") LoadPlugin("C:\Program Files (x86)\AviSynth+\plugins64+\mvtools2.dll") LoadPlugin("C:\Program Files (x86)\AviSynth+\plugins64+\svpflow1_64.dll") LoadPlugin("C:\Program Files (x86)\AviSynth+\plugins64+\svpflow2_64.dll")
C:\Program Files (x86)\AviSynth+\plugins64+\ is folder for plugins autoload.
What picture do you see in source video just after it is opened?
FFmpegSource2("clip.mp4").ConvertToYV12
I see a normal picture, then green artifacts the next, then back to normal picture (1-2-1-2..)