Happens when a different browser?

Try a factory reset and setup from scratch. 
Leave the default IP address alone for now. 

Update the RBS to v.21 FW version manually first. 

Then update the RBR to v.21 lastly. 

If all good here, I'd power cycle everything OFF for 1 minute then back ON. After all is good, then you could try your custom IP address string. 

Reason for recommending v.21 is that were seeing users post that there having issues with v.31 version of FW. So last good stable version is v.21. 

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NeoVN wrote:

My Orbi system is RBR 750 and 3 x RBS 750.

RBR was using as router.

3 x RBS connected with RBR using wire.

I was using fine when loading firmware 4.6.11.1

Few day ago. I tried to update firmware to 7.2.6.31. And from that day, my system had problems. I tried to downgarde the firmware back to 4.6.11.1 but the problems still there.

I cannot connect to my system. But all devices still can use wifi.

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