The filename I got is the same as yours, Microsoft_Rocketbox_master.zip, but it's 7 Gb (7,359,432 kb). It does not appear to be a multizip archive so far as I can tell.

Googling suggests there can be a lot of different reasons downloads can fail from Github. Everything from aggressive antivirus software to hardware issues. It looks like trying from a different computer, or using a different network, or using wifi instead of the ethernet card, often works.