Slow WiFi

Hi,

I have several Mikrotik devices in the network.
From RB2011, CCR1009, CRS125 and RB951G-2HnD.
Wired clients work great but wireless clients have slow connection.
If I look at the status in Windows it looks ook and see a connection of at least 144 Mbp/s
But by file transfere at the network I can’t get higher speed of 10 to 20 Mbp/s
Allso internet is very slow.
This is with connections to all mikrotik devices.
What can be the problem?

Without a network diagram and more specific details we won’t be able to point you to a troubleshooting path…

I understand and can provide a network digram.
What data do you need else?
It is all about clients who connect to a mikrotik (SW01, SW03, SW06, SW11, SW12, SW13 or SW16) have a slow connection.
Clients are all N devices. (laptops, Smartphones, Cameras)
TNW.JPG