AE Beta 17.1.4 Build 2 / FPS error

Steps to reproduce:
    1. Import movie .mp4 for rotoscoping
 Result:

movie is recognized as .AVI and is interpolated in rotobrush - produces green frames. (does not seem to be due to RotoBrush 2). 

Expected: ...

Green frames do not appear in previous versions of Ae 

previous versions of Ae have different frame rate interpreted.

System info
    Application: After Effects (Beta) v17.1.4.2
    OS: macOS v10.13.6, RAM: 128.00 GB, CPUs (logical): 36