CheckMK version 2.0.0P1 vs CheckMK version 2.0.0p16 (CRE): Agent takes nearly double time to answer

Is that the systemd-timesyncd bug?

Check if ntp or chrony are running on your hosts for time syncing and really disable systemd-timesyncd:

systemctl disable --now systemd-timesyncd
systemctl mask systemd-timesyncd