Take a look at the export functionality from Sketch to Zeplin.
It seems that I have to export twice before the image updates in Zeplin. I'm not sure if this is more of a bug than a suggestion but I thought I'd post it here regardless.
Hey guys, sorry about this. I believe this happens on large Sketch files. If you save and wait for a couple of seconds before exporting, that should solve the issue. We'll try to fix this soon.
Anthony Loven commented
This happens to me all the time. Sometimes it takes 3 or 4 tries for an artboard to finally make it to Zeplin.