I live in a house where some of the downstairs internal walls are solid (brick and block) but the upstairs walls are all stud. Since I bought the system it has been very unstable. For for some reason Tuesday mornings seem the worst. Particularly on a Tuesday it seems the internal nework has crashed overnight and some days it will crash midday without warning too. My wife has been working from home for the last 18 months and does a lot of MS Teams video conferences from that 1st floor front bedroom, so its highly inconvenient to have the network crash so frequently. The PC connected directly to the main DECO seems unaffected.

Main P9 is in the study at the back of house sat on a desk. Then I have an M5  in the kitchen high up on the wall, also a back of house room. The two rooms are separated by 1 stud and 1 cavity brick wall.

Next is the lounge P9, also back of house. This shows the signal source as the main deco and not the kitchen which is closer.

The 3 units across the back downstairs are virtually in a straight line of length about 15M but separated by walls.

In the back bedroom above the lounge P9 is a M3W.

In the front bedroom, same side of house as the back bedroom above is the last P9. The main Deco therefore is virtually on a  diagonal line through the centre of the house. This unit shows signal source as the lounge not the M3w which is closer.

The house is about 15M side to side and 12M front to back. I would have thought that 3 P9 units would have been enough to provide a reliable network but I added the M5 and then the M3W one at a time to improve reliability in the front upper bedroom but without success.

Anyone have any suggestions on how to improve reliability?  My next move is to buy a powerline set to see if that helps, but I've invested enough in TP-LInk hardware and am a bit reluctant to throw good money after bad.