With CM-12.1-20150518 I still faced stock browser problem on other mirrors, ODP download is not a problem though. Thanks.
Actually I have a feeling that it looks like when getting through many sub directories before downloading file, it lost memory or buffer to get through that layer, it turns back to original site. ODP download is not that complicated as other three mirrors which includes many ads as well. So I could download from ODP without any problem, but on other mirrors when gets to nightly sub directory it turns back to download origin. This fault phenomenon is also happen on CM-20150518 as well. Thanks.