Progress after a knee replacement is not a straight line. Weeks where nothing seems to improve - or where the knee even feels more stiff - are a normal part of the first year.
What matters is the trend over months, not the difference between yesterday and today. Keep the daily routine going through the flat weeks; that is exactly when it earns its keep.
If you feel stuck for several weeks in a row, or you are losing movement you previously had, that is a good reason to talk to a clinician - you can book an online appointment directly from the app.