@Joseph-TP  Hello 

I am using a wireless backhaul as I have a old house, so getting wires from the main unit to the next would require more work. (then use a ethernet cable to connect to my PC and console) It still does reboot (or I believe it's a reboot, I'm assuming reboot as it gets reported as 'offline') before 8pm, but it's less frequent, (last time it happened was a few minutes ago at around 15:30 BST). Where after 8pm it happens more frequently. 

I did have SMB share mode on, and have now turned it off all the sharing, i'll let you know if makes a difference at a later point.

I did not make any changes to the settings except for updating the firmware on all mesh routers (BE550, BE400 and AXE75) and the system worked perfectly fine, I have not added any new devices on the network, and the link between the BE550 and AXE75 is stable, as my brother connects to that router for work and he's not complained about drop-offs. 

The firmware is upto date on all the devices, with the main router being 1.2.3 Build 2026012. 

regards

H R Mohammed