I also reproduced the problem on v18.03. You must be getting intermittent results. For some reason, the combination of YADIF deinterlacer, Export > Video > Parallel processing, and this file format (MPEG-2 video with B-frames in MPEG-2 Transport Stream) is a particularly challenging combination. The workaround is to do one of in Export > Video:
- set Scan mode to Interlaced,
- turn off Parallel processing
- or use a different deinterlacer.