Long time FCP/Avid editor here but I'm new to Adobe Premiere. I saw a few threads on here dealing with errant white flashes on export but it seemed to be more like general artifacting. I notice the problem specifically when I'm using black video or graphic - but it only shows up on playback on an older Mac.
Here is an example of what my timeline looks like when I see the problem. V1 is a background, V2 is a green screen shot, and V3 is a bug. I've edited in a sencond of black video before the start of my content so I can have both layers fade in.
This latest time I encountered the problem I was using Premiere Pro CC 2015 and exporting to H264 via Media Encoder using the Vimeo 720pHD preset. I'm working on a PC although I've had the same problem with videos rendered on our Macs. What is truly mystifying to me is that these flashes do not show up in VLC, playback on PC, playback on a newer Mac (Mavericks) or on upload to Vimeo but the do show up in Quicktime or MPEG Streamclip on a Snow Leopard Mac. I know you could say "well throw out your ancient Mac" but I'd like to know why it's happening. Also producers and clients might have old Macs so I can't deliver videos like this.
Is it better to export a high resolution (Pro Res/DNXHD) master and then run it through Encoder instead of going direct to H264?
I had a similar problem when using encoder as well. I found that if my video renderer was not matching i.e. encoder was in CUDA mode and the application was in software mode, I got that problem. I fixed it by just exporting directly out of premiere.