Greetings!

Building

I'm working in a school with limited resources regarding AP-s. The building has 3 floors, which have L shaped corridors. 3 EAP245 v3 are installed on the first floor (the middle) in each corner of the L shape. Since for us these devices are expensive we extended the network with 2 routers configured to act like APs where the EAP245s reached poorly. These two routers are inside two rooms in the middle corner of the L shape. One is on the ground floor and one on the second floor (not exactly above/under the other). The EAP245s are out of the classrooms which have 0.5 meter thick walls towards the corridors. I cannot determine the thickness of the floors, but I experience these additional routers to have usually ideal signal in the classrooms on top of it or below. So I assume the walls are a factor in sometimes poor signal, or interference.

Config

The EAPs are providing both 2.4G and 5G (altough the latter is very rarely used). They use the same SSID and password to make users able to easily migrate from one to the other.

Each of the EAPs are configured to 20MHz and channel 1, 6, 11. Their Tx power is set to medium. This seemed to change the amount of interference I see on the EAP245 devices.

And here comes what I don't understand.

Question

I see very little amount of interference on the EAP245 devices on the right side panel when I click on them. (MAX 5% or lower) But when I check the Wi-Fi Traffic Distribution widget, I see that 2 of the 3 channels used either 1, 6, 11 are almost always yellow or red. The teachers use laptops, TVs and phones during classes. (Not in the IT room, that's wired, aka no problem). And a lot of times it seems to have some problem with the network even tho it has signal (sometimes that's lost too). Overtime I want to make at least the TVs wired but it's not today's menu. I just want to understand the difference I see on the statistic panels and what can cause the problem.

Thank you for your help in advance!