Hi,
It's interesting they have a formal monthly review system - this is unusual. Normally, PhD progress is evaluated internally on an annual basis.
A PhD is - to use the cliche - a PhD. It doesn't have grading; it doesn't track what happened along the way. It just is.
As a consequence, the only way internal reviews will impact it, is if the outcome is the University refuses to allow you to continue to study. It is not in the University's best interests to do this as they lose the fees and prospect of a completion; it's generally done on an ethical basis that there is no realistic prospect of you completing, and therefore it's wrong to allow you to continue.
I would think you can rest easy that unless your research itself is way off-track (as judged by your supervisory team), failing to file paperwork will not be a deal-breaker. Many students also worry about training-credit style systems, or other hurdles the Uni implements. Ultimately if you're doing good research and can complete, they will let you do so.
It is still preferable to file paperwork where you can, as admin-types will get pent up about it, but I've never seen someone fail a PhD on the basis of a missed monthly meeting or training exercise.