Anki can't sync with anki-sync-server (https://github.com/ankicommunity/anki-sync-server), due to this commit: https://git.archlinux.org/svntogit/community.git/commit/?h=packages/anki&id=fb9f1fc7f64ffc6a8b156a7f3a137d5ddb521ec9. The build hash is sent to the server, to check the compatibility (https://github.com/ankicommunity/anki-sync-server/blob/develop/ankisyncd/sync_app.py#L62). With anki 2.1.26-1, the client sends the version "arch-linux-2.1.26-1" in which the server matches "rc", thinks it's a release candidate and tries to compare the "h-linux-2.1.26-1" version. I've attached the corresponding server log. If the build hash must be unique for ArchLinux, maybe it should be prefixed with "al" or something that does not contain "rc" (or "alpha" or "beta").

When built without https://git.archlinux.org/svntogit/community.git/commit/?h=packages/anki&id=fb9f1fc7f64ffc6a8b156a7f3a137d5ddb521ec9, Anki tries to synchronize, but encounter a protocol compatibility issue. This is another issue, that has to be fixed in the server upstream.