@Kevin_Z
Ok here we go
I have a 2 floor home after climbing one stairs from the entrance door:
In the living room, right next to the modem, I have a main deco connected through a short but good quality wire (I’ve checked multiple wires to rule this out) to that modem which is in Bridge mode.
A mediabox from Ziggo is connected to the main deco as well to get wired data.
In the same living room I have another deco (slave 1) only 6 meters away from it, but without that slave, my Nest Hello doorbell downstairs couldn’t get a good enough signal. To this valve I have also connected a Philips Hue bridge to use multiple Hue lights throughout the house. On the same floor but all the way in the back of my house I have a dining room Deco (slave 2) to expand the network to the upstairs balcony on the top floor. I have an Apple Airport Timecapsule connected to this slave to run automatic backups. My house also has 2 google hubs and a Nest thermostat (in case this is relevant to know)
I have done the tests you’ve asked me to do and these are the results:
By the way, my ISP contract says I should get 250Mbps down and 25 up.
Wired laptop directly to modem I reach 250Mbps down and 25Mbps up (Ookla speedtest)
The link speed my laptop (MacBook Pro) tells me it has when wired to the main Deco is 1Gbit/s and when using wifi it says 300Mbit/s
When I wire my laptop to the main Deco and run the speedtest from Ookla I get only 6Mbps down and 25 up
After this I did multiple tests with the deco app while making sure my phone was connected to each deco separately
wifi main deco test 1: 20 down 25 up
wifi main deco test 2: 4.4 down 25 up
wifi main deco test 3: 7.5 down 25 up
wifi slave 1 test 1: 4 down 25 up
wifi slave 1 test 2: 8 down 25 up
wifi slave 1 test 3: 98 Mbps 25 up <- only fairly decent result
wifi slave 2 test 1: 9.5 down 25 up
wifi slave 2 test 2 16 down 25 up
wifi slave 2 test 3: 10 down 25 up
I’ve also tried to see what happens when I turn of my hue bridge, nest hello and Timecapsule
Ookla results after that was 3 down and 25 up
Deco app said (after 3 tries: 23, 1.7 and 5.5
So that didn’t help either and neither did changing the DNS servers and clearing the QoS and high priority stuff.