GT-BE98 pro slow 14-15MB Wi-Fi file transfer speed from USB3 drive on router

[snakebite3]

The transfer speed on LAN to my USB 3 attached to router is over 100MB, however the speed over wifi is capped at 15MB no matter which band I use. I tried on my Desktop(5Ghz 3x3),Phone(5Ghz) and Tablet(6Ghz) same results. Is there a reason for this? I using SMB and FTP. The firmware is the stock Asus 3.0.0.6.102_37812.
I want to clarify this is using Asus USB apps server center.

 

[muzykcb]

I have RT-BE86U - it's the same. It's a software fault, I restored factory settings and it helped, now I have 80MB/S for a while but after a minute it drops to 40MB\S and stays that way.

In the previous RT-AX86U it worked properly all the time 80MB/S