You miss fping which is installed by default and used by armbianmonitor to check network availability (uploading).
Go ahead, install it and try armbianmonitor -u.
The only other possible explanation I can think of not reaching NTP servers is that your ISP is blocking remote NTP servers (DDOS mitigation), that happens rarely, is easily checked by 'ntpdate -vd pool.ntp.org' (non privileged port, so not blocked), or even simpler, use your gateway ip as most routers broadcast it anyway.