https://github.com/Montecri/GPSTimeServer/blob/b72ee8c58b891f41e3a836fae0de9ad482129ad0/src/main.cpp#L385
That is implausible, why greater than 3000. So there is wrong time for a few seconds when booting up!
if (age < 1000)
is the better way, the issue is gone. ;)
cu