Do you use level of compression = 0 when you make output of animation in PNG Sequence?
There is field Compression in Blender. Available values from 0 to 100.
If to move cursor to this field explanation appears:
Amount of time to determine best compression: 0 = no compression with fast file output, 100 = maximum lossless compression with slow file output.
I work in Windows 10 Home 64-bit. Blender 2.79. Cycles Render.