Okay - I think I understand a bit better now. (I may have made some misstatements before because didn't understand your situation/your situation wasn't explained well).
Keep in mind some of what seem's going on right now is specific (it seems) to India and covid matters.
To give some background: for non-family sponsorship applications, up-front medicals are reasonably common. (I don't follow most of those types of applications).
To do a NEW family sponsorship application, the instructions say NOT to do an upfront medical. Instead they should wait for the medical request. Standard advice here is: follow the instructions.
[One reason I was a bit confused by your posts and questions is that there are often posters here for spousal who want to do up-front because they believe / someone told them that it would make things faster. (It probably doesn't and IRCC doesn't have to accept the results - but people still believe it.) Also posters sometimes say "they" told them they could or should do upfront. (Often not clear who the 'they' is or if they did speak to someone from IRCC, it was call center - and then it becomes unclear whether the caller actually asked the right question).]
I think what is happening is what was described above: NDVO and other offices are only catching up; they have limited capacity to just keep issuing re-medical instructions. Hence it seems someone told you to go to a medical center and say it is 'upfront.' (IRCC will link it later with the UCI). It's not actually an upfront exam - because not for a new app - but (for simplicity's sake) the medical center only has two categories - upfront or with medical instruction.
BUT: for covid-related reasons, the medical centres seem to have limited capacity. So they may be saying they are not doing upfront exams i.e. they require a medical request from IRCC to book you. (Logical with limited capacity to say we will only do exams that are required.)
I don't have a solution for you: wait or keep trying to get the medical request letter from IRCC, or, keep trying the medical centers where you are and book under an 'upfront' examination when they will allow it.
