Can other devices on the same network access NTP? If not, it may be your router. My 'Shake seem to have no issues with internal or external servers:
C:\Windows\System32>ntpq -pn raspi-14
remote refid st t when poll reach delay offset jitter
*192.168.0.20 .GPS. 1 u 2 32 377 1.479 -0.005 0.273
+192.168.0.3 .kPPS. 1 u - 32 377 2.151 +0.080 0.680
+192.168.0.71 .kPPS. 1 u 16 32 377 2.153 +0.177 0.498
uk.pool.ntp.org .POOL. 16 p - 64 0 0.000 +0.000 0.001
-217.114.59.66 157.44.176.4 2 u 57 64 377 19.060 +3.108 1.835
-162.159.200.1 10.21.8.19 3 u 35 64 377 23.336 +1.530 1.182
-217.114.59.3 33.117.170.50 2 u 44 64 377 19.299 +2.699 1.055
-162.159.200.123 10.21.8.19 3 u 4 64 377 23.796 +1.701 2.229
-217.155.2.22 17.253.34.123 2 u 7 64 377 38.074 +2.607 3.210
-51.155.16.62 .GPS. 1 u 20 64 377 34.692 +2.816 1.254
I’m using NTP 4.2.8p11 which is out of date, I know, but that shouldn’t affect connectivity.
C:\Windows\System32>ntpq -crv raspi-14
associd=0 status=0618 leap_none, sync_ntp, 1 event, no_sys_peer,
version=“ntpd [email protected] Wed Feb 28 09:21:50 UTC 2018 (1)”,
processor=“armv7l”, system=“Linux/4.4.26-v7+”, leap=00, stratum=2,
precision=-20, rootdelay=1.479, rootdisp=3.944, refid=192.168.0.20,
reftime=e2c9134a.682c5617 Mon, Jul 27 2020 9:48:10.406,
clock=e2c91403.b6707f11 Mon, Jul 27 2020 9:51:15.712, peer=19584, tc=5,
mintc=3, offset=-0.005358, frequency=-1.522, sys_jitter=0.256177,
clk_jitter=0.274, clk_wander=0.127