Router child device limit = 4 reached?

[ymatsigin]

Hi all!
There is a small Zigbee Network with about 30 devices in my house. Basically aqara motion detection, temperature and water leak sensors. Plus some radiator thermostats. All devices are spread across 180m2 house, thats why I use some routers for extending my network:

• 4x LLKZMK11LM Aqara relays with router function
• 2x GWRJN5169 Aqara Zigbee Hubs, rooted, openWrt, flashed with ZigBee chip router firmware (https://github.com/igo-r/Lumi-Router-JN5169).

Coordinator: Egony Zigbee Dongle Stick v4 CC2652P (Ebyte E72-2G4M20S1E)

Everything flashed with latest firmware.
Adding new devices I've mentioned only 4 clients per router are adding, all next devices go to next (but not closest) router with less than 4 connections.
And now I finally have a situation when all the routers covering a place with no signal from coordinator are with 4 clients and new devices there cannot be added. Nothing is shown in logs (debug level), nothing is added.
The only way is to place device near coordinator or last "free" router, in this case everything works fine, but it's not the target device location.

And I think - that's strange that all my routers have connection limit=4. Also in coordinator mode Aqara Hubs can hold lots of devices. Have found nothing in manuals and in firmware description.

Maybe there's a kind of setting that can increase a number for child devices for my routers?

Attaching map for info