ntp Stopped Working

ntpd has suddenly stopped working. The daemon seems unable to reach NIST or Google time servers. All other ordinary network functions are OK. I'm almost ready to reinstall ntp as a last resort. Meanwhile I'm using htpdate. Any ideas of what's happened?

System:
Host: hound Kernel: 5.8.0-44-generic x86_64 bits: 64
Desktop: Cinnamon 4.8.6 Distro: Linux Mint 20.1 Ulyssa