Zstack behavior on Different Router and Coordinator channel

When a router never joins any Zigbee network, it would send beacon requests on the channels that you set. When it finds there is a coordinator on channel 20 with permit join enable, it will try to associate with it.

Problem is network is partitioned and has a loop which I don't get it. there are total 5 routers:

R2,R3,R4 have R5 as their parent (joined on Ch15.)
R5 has R2 as it's parent on Ch15.(R2 and R5 are both parents of each other!)
R1 has Coordinator(0x0000) as it's parent on Ch20.

But there is no connection between R1 and either of R2-R5.
All are on same PANID.

From your descriptions, your coordinator with R1 and R2-R5 seems on different Zigbee networks. I don't understand what is your point.

Yes, I would agree with YK. The network seems to have been commissioned strangely.
If you started from a factory reset system, with an open channel mask of 15, 20 and 25 then you should have your coordinator and routers all on the same channels.
It looks you have two different PANs.
Thanks,
TheDarkSide

They are all in same PANID. Only R1 has a coordinator. R2-R5 doesn't have coordinator. also R2 is parent for R5 and R5 is parent for R2. Which is confusing.

If there is no coordinator for R2-R5, who create R2-R5 Zigbee network?

That's why I am confused. None of them has Coord (0x0000) as parent.