iPhone upload speed slow on Unifi 7 Pro Wi-Fi network

Hello!

We have built a wifi network consisting of Unifi 7 Pro, consisting of 20 APs. We plan to expand it further, up to about 150 APs.

However, we have found a problem that we cannot influence: The upload speed of the iPhones is very slow. Max. 4 Mbit/s instead of 100 Mbit/s. We have a leased internet line. It works perfectly on Android, Linux, and also works well on Windows.

There are only problems with the iPhones. And all devices are running on the latest firmware, and the iPhones are running the latest IOS version

We have tried everything from channel allocation to iPhone settings.

The upload speed does not go above 5 Mbit/s.

So we should think about whether to continue building the wifi network with these devices.

Does anyone know a solution to this?