Make sure your AE is completely up to date. Flush disk cache often. Render to a DI (digital intermediate) to a production codec and compress for delivery using the Adobe Media Encoder.
Thank you for the quick response, Rick. My problem is I'm rendering videos to use in other AE projects, so I want to isolate the problem. Is it rendering from ProRes (422 or 4444) or rendering to a ProRes codec or both? It only happens where the lens blur effect is used, so is that a part of the problem?
In order to help anyone else, who like me is still having the After Effects CC red frame glitch, even with the most up to date version which is currently 12.2, Here are the results of my tests:
I received red frames when my source material was animation codec rendering to ProRes 4444. I also got red frames when rendering from ProRes 422 to a PNG sequence. I did not try Rick's suggestion of rendering from an Intermediate codec because my expert told me that the quality wasn't high enough for what I am doing. But I will try that and report back my findings.
What did prevent the red frames was turning off the effects "lens blur" and "keylight." So it appears that it is those effects (and perhaps others) that are the culprit. I could work around keylight, but I don't have any acceptable alternatives for lens blur, so my solution is to do this particular work in CS6 and hope that Adobe is continuing to try to solve this problem in CC.
I have the "same" issue with the red frames in AFX CC
I have seen them first, as I resized a prores4444 HD to a smaller format and saw the redframes in the preview window.
Setup in AFX: I created a comp from the HD Prores4444 footage and put this comp in a comp with resolution of 960x540.
The output format was again prores4444.
I shuttled through the clips in the small comp and I saw the red frames too.
When I switched to the HD comp at the same position everything was fine.
I "solved" the problem by flushing the cache, twice. Because after the first purge I was only able to render the first clip. The second one had the red frame problematic again.
Maybe It has something to do with hardware accelerated layers.
I'm using a MacPro running OSX 10.8.5 with a Nvidia GTX680.
I am having a related issue, but possibly more vexing. I am working from ProRes 422 source footage in compositions sent via Automatic Duck XMLs, rendering back to ProRes 422. I noticed a random red flash on one of my renders. I get them fairly often in Premiere Pro CC and Media Encoder, so I assumed some simple changes and re-rendering would fix the problem. Sure enough, the red flash showed up again on the exact same frame. I checked that frame in the comp. It's there pre-render as well. I turned off all other layers and removed all effects. Still there. I opened the layer. The red frame is there. Then I opened the source clip from the project pane. The red flash is there, too. But if I reveal the source footage in the Finder and open in QT, there's no flash.