Sorry for some delay with reply. I was not able to find an AppVeyor account by email you use on the forum to investigate specific builds, so links to the failed builds would be helpful.
Answering your question -- we have no ongoing network problems now. However I must say that networking issues are very difficult to reason about. It can happen on both ends and in between. Your local machines can have a different route to the target servers or just hit different front-end/CDN servers that AppVeyor build VMs.
To be on the safe side I would recommend to add a retry. If you add appveyor-retry before commands which behave flaky, you should greatly decrease error rate.