So here is what i did. I take a frame. I freeze time it. Then I stretch it. And then I duplicated and masked or masked and duplicated and removed the mask. Only later I realize that these black dashes appear. They appear in the rendered output as well. It has never happened. I deleted the files and re-did the masking and things, it worked. But just in case for the future, i want to know, how this happened?
Btw. this is a linked composition from premiere pro.
Well, check your effects. This looks to me like you are using some Write-on or Vegas effect.