black patch appears on screen (After Effects)

[Shane5E25]

i'm not sure how it happened but while trying to render my video without getting an error, this black patch appears in my precomp and won't go away. I went into previous save files and it still appears. i'm not sure what happend and i can't find anyone with this problem. After Effects 2020, clip uses rotobrush 2, Macbook pro (late 2013), 16 GB of ram

[OussK]

Did you try to purge your Memory and disc cache? 

[Rick Gerard · Accepted solution]

To figure out where your black spot is coming from start by enabling the transparency grid, then start soloing layers that are under the CTI (current time indicator). I can only see two layers under the CTI in the screenshot, one is a Null and the other is a nested comp (pre-comp). Neither layer has effects applied, the Null, layer 17, is the parent of the nested comp, 18 so the only thing that makes sense is that the null is used to animate the position of layer 18 and that would not cause the black spot, which is probably transparency, to appear in the Comp Panel. You'll have to open up the timeline for Pre-comp 1 Comp 1 and look for the problem there. You will have to select all layers in that comp, start soloing them, checking for all modified properties by pressing the 'u' key twice, and turning on and off effects, and resetting properties. It doesn't look like you are giving your layers meaningful names either. That is not going to help you dig through the project and figure out what is going on. If there are other layers under the CTI that are not showing in the screenshot, you'll also have to dig through them.

Comp 2 is twenty minutes and thirty seconds long so that tells me you are using After Effects as a video editor. AE was never designed for that. You are asking for problems that are difficult to solve and asking for render failures. After Effects designed for and well suited to produce visual effects shots, motion graphics, and animations that you cannot produce in an NLE like Premiere Pro. Most comps should be a single visual effect shot or a short animated sequence that is no longer than a single phrase or sentence of dialogue or narration. 

When you find the problem with the comp used as Layer 18 you should seriously consider rendering that comp using a visually lossless production format and replacing Layer 18 and/or the other layers under the CTI with the rendered footage. 

[Shane5E25]

Thank you!! I'm sorry if anything seems unorganised, i'm a beginner to After Effects and Premiere Pro, so this helps out a lot.