Greetings!

What (possibly) there are restrictions or recommendations for system configuration on 4 (5) APs of the RouterBOARD wAP 2nD AP (installed “in line”) and about 40 devices (Android smartphones).
The primary system configuration was based on RB760iGS (may now be replaced).
The whole system is planned for working with sports (entering results in the client program on smartphones and transferring them to the referee server for calculation and processing).
The first option (refused) was based on CAPsMAN and a seamless pattern.
A currently used is "separate" system (different channel`s and different SSID for all АР)
But the system works differently in different locations (relatively stable or very bad).
Settings (in Mikrotik device`s) not changed, "client`s" devices the same all the time.

P.S.
All client devices begin to transmit data at the same time (approximately every 5 minutes) - the rest of the time they are in "ready" mode.

ADD/UPD
Distance from AP place and Android device max 25 meters (but usually 2-5)

In post attachment device with Red "border" = not connected, Green = connected to any access point, (priority over the nearest)

Still puzzled by your topic, I'll just leave my two cents...

• wAP 2nD AP is 2G only, don't you want/need 5G (as well)?
• Why was CAPSMAN refused?
• Why use different SSID's? Wouldn't it make sense to have a single (and well configured => turn down transmission power) network?
• Different channels is a must, be aware that:
  • the 2G band is completely (over)saturated
  • you can only choose 1, 6 and 11 as non-overlapping channels

To have a proper functioning WiFi network you have to do a site survey. This is the only way to be able to set best channels.

I agree with above. The system will not work well because 2GHz simply doesn't work well in scenarios with many devices. CAPsMAN and one single SSID for 2 AND 5GHz is the only workable solution. The chosen scenario, I can't imagine how to expect anything better. You get what you chose

Still puzzled by your topic, I'll just leave my two cents...
Thank`s

• wAP 2nD AP is 2G only, don't you want/need 5G (as well)?
  Price... (~ x2)
• Why was CAPSMAN refused?
  For more stability (in the first version we tried this option (but the system turned out to be sensitive)).
• Why use different SSID's? Wouldn't it make sense to have a single (and well configured => turn down transmission power) network?
  Some functionality of the judging program (it is possible to bind MAC address groups to specific access points) + channel adjustment (search for free channels and frequency shift)
  
• Different channels is a must, be aware that:
  • the 2G band is completely (over)saturated
  • you can only choose 1, 6 and 11 as non-overlapping channels

To have a proper functioning WiFi network you have to do a site survey. This is the only way to be able to set best channels.
Yes ! (I indicated this reason a little earlier, "Archer-E" work in another gym (behind a metal wall))

I agree with above. The system will not work well because 2GHz simply doesn't work well in scenarios with many devices. CAPsMAN and one single SSID for 2 AND 5GHz is the only workable solution. The chosen scenario, I can't imagine how to expect anything better. You get what you chose

It may well be BUT!
we used this system on the outdoor competition`s (4 access points worked in one area) - the circuit worked well.

Used this system in the hall (more precisely two - 2 access points on one floor, 2 more on the next, all points were visible on the devices (but the difference in signal strength was more noticeable).
The system worked just as confidently.

It may well be that these were "extreme regimes." I do not know.

To have a proper functioning WiFi network you have to do a site survey. This is the only way to be able to set best channels.

May I make a suggestion? From the RF engineering perspective, you can clear up the acjacent channel interference (remember the carriers have RF skirts and RF reflections off non-conductors and conductors in an enclosed space) greatly by not using the default antennas used in the wireless access points. I do have some very good experience in antenna design for 2.4GHz 30-50 km line of sight (you call this 2G, I think) and also 6/4 GHz, so the same basic principles would apply - with Mikrotik devices. Can you inspect your hardware/change the hardware type to use external antennas - to reduce the radiation pattern and side-lobes in vertical and horizontal directions. Explore the concepts of zones by adjusting the radiation pattern of the antennas by RF absorption (signal loss) or reflection (signal gain). I would absolutely in this open environment (thanks to the picture) use the lowest minimum power, and the tightest beam confinement antenna I can find, or construct, and I would expect to receive signals from APs all over the floor, depending upon the RF propogation/reflection. Only thing is that the RF noise floor would be better as the RF being transmitted in the area of interest would be more or less confined to that.

I'm curious if you experimented with a single SSID, lets CapsMan manage the frequencies (it listens and adjusts frequency assignments) and then on your DHCP server assign different groups to different subnets (as you will be exceeding 255 users easily) or different VLANs/subnet combinations - and shoot for a lower TX power to not saturate the RX antennas nearby when they are trying to receive all the small devices TX.

May I make a suggestion? From the RF engineering perspective, you can clear up the acjacent channel interference (remember the carriers have RF skirts and RF reflections off non-conductors and conductors in an enclosed space) greatly by not using the default antennas used in the wireless access points.
SKIP by HopLiteAir

I understand your idea, it is quite reasonable.
But I have suspicions about other reasons (I do not speak English very well, so I can not describe the observations in detail).

At these competitions, the participants are young people who use their gadgets a lot.
When checking the radio (using the WI-FI analyzer application), a situation was encountered with a very dense network of devices in broadcasting.
But even after the end of the day, when the participants dispersed and the air became "clean", our equipment did not start to work efficiently.

In the day time (the wi-fi analyzer application) it sometimes showed strange situations, part of the AP (Archers-X) worked at the same level, and part could "fall" to the zero level, and rise again after 5-10-15 seconds. Perhaps this is the features of the application.

Plus, I experimented with connecting my smartphone (xiaomi) to any access points, my smartphone made the connection / authorization much faster and more stable.

Maybe you need to try different combinations of configurations in the equipment settings.

Therefore, I wanted to know if there are any features or limitations in the operation of these access points when connecting a group (we tried to use one access point in a separate room, but at the “only connection” level, the process of connecting all 40 devices was quick).

P.S.
Perhaps it is in this sports facility that there is interference (?!) That affects the operation of radio equipment.
I met a similar situation when my radio remote control for a my DSLR was inoperative due to a wireless fire alarm system (433MHz)