Or there is something wrong with your network? Are you try to use the wireless network for this?? Please check/provide:
1. Is your server already downloading something
2. Did you notice this right after install? We are downloading package base updates in the background in the first run
3. Results of network testings.
Remember that you are using a mainline (NEXT) kernel which does not have all functions yet. If you want them, you need to use a default/stock kernel, found in Android or TinkerOS, which is anyway not recommended for this case. And for many others as well. You can switch kernels back and forth in armbian-config menu.