Long delay before the remote desktop appears

Question

Hi,

We have a 5 RDS farm with a broker. The server is recent. There are no resource problems: everything is below 30% avg utilization (less than 10% for the broker) andvhdx are stored on ssd storage. All works fine.
BUT, for a few months, when we start a remote desktop session, we see the classic start screen with all the "apply..." messages. and then, we have to wait 10 to 30 secondes in front of a black screen before desktop appears. I said "for a few months" because it was much faster before.

Our provider tells us that this is normal but does not give us the reason why it's suddenly slow.

In your experience, is it normal to have to wait so long before we can access our remote office, especially considering that it was almost instantaneous before?

Thanks