Import from an exsiting gitlab with url failed

Hi, i had an old version gitlab server 10.3.5, and a new version gitlab server 12.1.3. When i import project from new version to old version by using url, it always failed, and the application.log has the message like August 08, 2019 13:57: The Lfs import process failed. 5:GetRepoPath: not a git repository '/data/gitlab/git-data/repositories/base/service.git' . When i check the repositories folder, i found that there is only .wiki.git Any help is great, thanks.