@jes_ON
In your experience, have there been cases where the review required turns into approval without any action from the applicant?
Yes. First-level assessors sometimes make mistakes that are corrected in review.
Does the officer always request additional documents during the review?
No, not always. They can either request documents if they feel there is insufficient evidence of a claim, or if they feel there are inconsistencies or credibility problems.
Or is it always at the officer's discretion to approve/reject the application as is, without asking for clarification?
It depends on what the issues are with the application.
CIC agent told me today my eligibility has review required so I am obviously quite worried... have since applied for GCMS but.. any clarification you can provide would be helpful to calm nerves.
Eligibility review is very common, it just means the frontline assessor couldn´t make the call and kicked it upstairs. it does not necessarily indicate something bad about your application. There´s nothing to do until you get your GCMS notes.