Hi claudia2586, change the wireless channel on your router to avoid interference. Preferred channels to use are 1, 6, 9
and 11 since they're considered as non-overlapping channels. You can use the links below.
Changing the wireless channel on a Linksys router Manually:
http://kb.linksys.com/Linksys/ukp.aspx?pid=80&vw=1&articleid=4009
Changing the basic wireless settings of your Linksys Smart Wi-Fi Router using your Linksys Smart Wi-Fi Account:
http://kb.linksys.com/Linksys/ukp.aspx?pid=80&vw=1&articleid=25807
If that doesn't help, then you can also roll the firmware back to the previous version but before doing that please follow Vince_02 recommended steps first:
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Before trying to roll back to the previous version, can you try to power cycle the entire network and observe if you will still experience intermittent connection in the 2.4Ghz band?
-Turn everything off (modem, router, turn off Wi-Fi on mobile devices), wait for 10secs
-Turn the modem on, wait for 30secs to give the modem time to get internet from ISP
-Turn the router on, wait for 30secs to give it to boot and get connection from the modem
-Turn on Wi-Fi on your mobile devices and observe the performance
You can also try to hard reset the router and run setup. Let me know the results.
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I found his post here: http://community.linksys.com/t5/Wireless-Routers/EA6900-New-Firmware-1-1-42-158863/m-p/777443/highlight/false#M269333