Mesh - GuestWiFi - IoT - MerlinWRT - 2.4ghz issues

[cyberbooster]

Hello,
I'm struggling with understanding what is my exact issue here. If anybody has any clue, please send me a lifeline, thank you.

A bit of background
I have a 2 story house with 4 nodes:

• AX88U cable connected to starlink main router (on the upper floor)
• 2x AX86U Pro as mesh node (one on the upper floor, one on the ground floor)
• 1x AX58U as mesh node (on the ground floor)

My Wifi setup:

• a main WiFi (5Ghz and 2.4ghz) which works like a charm, no issues whatsoever, coverage is good both inside and outside my home
• a 5Ghz GuestWiFi which works perfectly as above
• a 2.4Ghz WiFi for IoT devices that is giving me headaches.

What works over the IoT wifi:

• a solar inverter SolarEdge
• a Tesla battery pack and gateway (the futhest point away outside of the house)

What works with issues:

• iPhone connects and can navigate, but has frequent disconnection and poor reception/bandwidth even close to the nodes. IoT Wifi shows up on the phone at times, not everytime I check in the settings, I have to switch off and on again the wifi few times to make it show up.

What doesn't work over the IoT wifi:

• NetAtmo Thermostat 5m away from AX86U Pro node -> recognize the wifi after several tries, connects, but can't setup
• Tado Thermostat 2m away from either node (tried getting close to everyone) -> recognize the wifi after several tries, connects, but can't setup
• Samsung dryer closer than the working devices (but behind a thick wall), doesn't even get a single bar of signal. In the same room the iPhone detects 5Ghz wifi, but not 2.4Ghz.

What I tried:

• standard firmware, updated to Merlin 3004.388.8_2 (no changes)
• changing roaming -db sensitivity (-75, -80, -60, -68)
• changing beamfoaming, MiMo settings, Bluetooth coexistence

What I'm uncapable of making it work

• For the life of me, I can't make SSH login work. On win10, I tried with native SSH, Putty, nothing connects. My guess I really don't understand how to make it work with the SSH keys, but even simple user/pwd doesn't seem to work.

My current config: