Comment by toniti

I recommend you to upgrade to BuildKit. Also, the above isn't really true for Docker CLI, mtime was never taken into account in the old builder and Docker CLI never sends uname/gname. With API it was possible in the old builder though (hence the incompatibility with compose for example). In more practical cases I've seen it caused by git directory instead, that isn't stable. In that case, you can put .git into .dockerignore or if you don't use it, BuildKit will discard it automatically.