Multy m1 Internet speed fluctuation

I am using it as a wireless mesh and the first device has a wired connection, but the speed drops on its own, and the same is true for other devices. Signal strengths between -65dbm and -70dbm There are no signal interrupters, but the speed still drops

This normal Speed my internet 100/50 mgbit

Last Device loses too much speed

Salon device gives low speed and last device gives normal speed

What is the cause of this situation, even with a wired connection, I experience a speed drop

There seems to be a software problem