I haven't got any request for additional documents as I have submitted everything at the time of application. All required documents from check list and some through my knowledge what they usually ask for while processing like funds and medical.
It's good sign they asked what they need instead of refusal, you can submit that again if it's in regional language and translation. One reason could be you might summited either only translation or only original at the time of application.
I have received COPR so I never need to extend it, but I think AOR and Nomination with checklist documents should be good, still you can ask to IRCC agent on call. you might check this link if you haven't already...
I have submitted everything with application (previously done Medical and Biometrics) so I have no idea about any additional documents timings, but if you have one, you can submit with web form before they ask if you haven't provided to speed up the process.
You will receive an another email with AOR, It states, you must link your application with GC key to continue processing. https://www.canada.ca/en/immigration-refugees-citizenship/services/application/account/link-paper-online.html
If you choose not to link your application:
It could take us...
There is a temporary medical policy that if you have completed within last 5 years you might be exempt from doing it again. Check the detailed info in the link https://www.canada.ca/en/immigration-refugees-citizenship/services/application/medical-police/medical-exams.html
Ghost update : there will be an update on your GC Key says application profile/updated but you won't see any other changes in the application. Some one reviewed your application and is going to further steps. You will probably see a message in your application in application status.
MP : Medical...
For inland AOR is not actually a letter, it's an email that will provide and application number and confirm that application has been received. There will be an another email as well to link your application with GC Key. Check this post...
Did anyone received PR Card recently? Who have received COPR, how long did it take to get PR card. Is the process same for all streams? It's showing 4 to 6 weeks but I want to know the actual time.