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That must be it. Thanks for the suggestion, Dave! I'll give it a shot 
Speed changes in Premiere Pro do not come into After Effects. Neither do effects. If you need to bring in a clip do it before speed changes or render and replace in Premiere Pro. Almost every time I use Dynamic Link in Premiere Pro to create a comp in After Effects I undo the action in Premiere Pro restoring the original clip in the sequence right after I save the AEP project I then complete my work in After Effects, render the shot, and then create a new bin in PPro just for effects shots, import the rendered (using a suitable production format and NEVER an mp4) comp and just drop it in the PPro Sequence right above the original shot. This is EZ, safe, eliminates rendering problems, speeds up the editing process in Premiere Pro in the long run, makes it much easier to make changes later, saves you time, and, in spite of sounding like more work, is easier and more dependable. The ONLY shots in a Premiere Pro sequence that I keep as a Dynamic Link are short shots with minimal effects that will render and preview nearly in real time. In the last seven or eight projects, I completed had visual effects on about 1/3 of the shots and not one of them was just a Dynamic Link. They were all rendered in AE. The timeline of one of the projects looks like this:
See the note on removing the outlet? If this complex composite was all dynamic link the likelihood of a problem would have gone up about 10 fold because of everything involved in the shot. Because it was a comp all I did was open finder and give a new name to the Find a loan.mov, open the AEP, remove the outlet, add the comp to the render cue and hit render, wait about 10 minutes, open up Premiere Pro and render the final movie for distribution. If the client needed to see just this shot for approval that would have not taken any extra time to speak of.
Now let's move on to a possible solution to your problem. First, let me ask a question. Have you used Rotobrush before and do you completely understand the process? If the answer is no to either part of that question you have some homework to do. I suspect that you are not familiar with all of the recommendations because your Layer Panel is at 50% magnification factor and the Comp Panel resolution is set to Auto. Rotobrush should only be done at 100% and Full Resolution. I also see you have Stereo Mixer applied to the layer. Rotobrush should be the only effect applied to the layer. If you need to use other effects add them, pre-compose, then use Rotobrush on the Nested Comp.
The first thing to do is to check the frame rate of the clip in the Project Panel. Make sure that the comp matches this frame rate or create a comp from the clip.
Select the footage in the timeline and then choose RotoBrush. Make sure the Layer panel, not the Footage Panel is active. Try selecting any point on the footage. If you have problems go back to the Main Comp and Pre-compose the footage layer moving all attributes to the new composition. Then Right Click on the Pre-comp (nested comp) and select open Layer Panel and try again.
When you get the layer panel open, select the Paint workspace so you have easy access to all the tools, choose the Rotobrush tool (Alt/Option + w) adjust your brush size and paint away. It took me 5 brush strokes to get here so it is not the image that is causing the problem. I just screen captured a still from your YouTube video:
You can see all the modified properties of the layer.
The best practice is to use Rotobrush on a separate comp and then when you have the matte generated, if the shot is longer than just a couple of seconds, Render the footage with an alpha channel or render just the black and white alpha channel and use that in your main comp.
If you insist on using Rotobrush in a Dynamic Link project you absolutely must make sure you Freeze the roto or render and replace the Rotobrush layer in the comp. If you do not Premiere pro will be using a background instance of After Effects that does not use GPU supported effects or much of anything else to propagate Rotobrush again in the background, which is slow and probably inaccurate, is prone to other failures, and it's going to take forever and a day to render a preview and then the final product.
Last tip. I don't know what format the original footage is but if it is a prosumer or professional camera you should have no problems. If it came from a consumer camera then it may be a very good idea to render a digital intermediate (DI) using a Mezzanine format (visually lossless) before you start doing any serious compositing.
If matching the frame rate of the comp to the original frame rate of the footage does not fix the problem, or Pre-composing making sure you move all attributes to the new comp does not solve the problem then you have GPU issues and need to check your drivers or disable it, AE is not up to date, or you have not followed the user guide.
I'm not sure what all you want to separate from the background but if it is just a sky replacement I probably would have used a Procedural Matte instead of Rotobrush.
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