rb 433ah drop tx/rx rate

RouterOS Wireless Networking
1

Hello,
I have a problem with RB433AH with 3 RB52 inside, 17 dBi sectorial antenas.
17 customers connected to the 3 access points.
at a time, some customers are rx rate droped to 1Mbs
what is this issue?

wireless table.png
wireless table 2.png