Hi, I have met the same situation here.
I completed my upfront medical 4 days before I received the remedical requested letter from IRCC.
Then I sent my upfront medical sheet to IRCC through webform multiple times. But my account still became “we didn't receive your medical".
So I asked their social media team, they said I'm on the right track. Also, the webform team confirmed that they have forwarded my medical to the right office. All I have to do is wait.
Sadly, this state lasted for 2 months. Then IRCC requested for my remedical sheet again, but this time, I can submit my sheet through my account instead of the webform.
Only took a few hours, my account became "you've passed your medical". And I got PPR about 2 - 3 weeks later.