I've had this problem before too but I couldn't find a concrete resolution. I'm running Yosemite 10.10.2 with the latest version being 10.10.5. Since I've had some wireless connectivity issues with the present version, I thought it would be wise enough to install the latest version and see if the issue has been totally dealt with. But every time I resume the download (since the whole package is some 2.36 GB), the Appstore resets it to around 50 MB and all that was downloaded goes to waste. Now I want some advice on how to stop this annoyance.