Never mined before,useless with any kind of programming,dont know if this is of any use to more experienced people.
I have ten MLDs running on a win10 desktop using modded usb2 hubs with 140 amp power supply spliced in.
I also had the problem, where 1 MLD would drop to 2 -2.5 Mhs for no apparent reason. Power was not the problem-plenty of spare,could not find any problem with connections,until I changed the usb leads from the hubs to the pc.
It seems it was an intermittent or damaged data lead,or possibly shield.
The old leads read fine on a meter.
All 10 now running rock solid at 876Mhz.