Control records state will move from "monitor" to "attest" and says updated by "system"
Due to an OOB schedule job
This is an expected behavior.
As per the script in the scheduled job: "Control attestation nightly run", line no. 14
var frequency = control.profile.attestation_frequency + '';
When you check this field by configuring through the form layout, it's having the value as "Quarterly" (depending on what value you provided), that's why the script is using this value and updating the attestation to 3 months.