I've had the exact same issue. 2.4 GHz network is disappearing. Tech Support emailed me and said to change the encryption to TKIP for the networks. I got a text from my wife who is home and said the Google Hub display is not connected to the network. I do not believe that this will fix the issue. Any help would be greatly appreciated.

@cy9394 I also have the same setup as you running my fios modem like you. Are you saying just to unplug the power on the fios modem and tp link router and the issue will be resolved? Any help would be greatly aprreciated. Thanks.

@harshakavuri 

I just wanted to share my recent C5400 experience. Purchased from amazon and 8 months later one of the 5ghz bands would not hold any speed and the only way to fix it would be to do a hard reset. It would work for a couple of days and then go back to not working, sound familiar. Anyway long story short TP Link's technical support via, chat, email, and remote access throughly analyzed the router and if you have the patience they will replace the router. I just recieved the replacement which is a C5400X, it's a gaming router and it's a beast. They must have had a bad batch of the C5400 cause I'm not the only one who got the upgrade. Good luck with everything 

@wolfpacker 

I'm on RMA number four, hopefully. This is C5400 router number three.  Original router was replaced on RMA, but it, router two, had a loose screw inside that was an electrical hazard. I asked for a new in box replacement and was sent router three which now has intermittent 2.4 Ghz connectivity and no 5 Ghz ch1 radio. I also cannot connect to 5Ghz ch2 even though it can be seen.

Right now I'm back to usin my old Netgear router. 

@wolfpacker 

I have the same issue.

@harshakavuri 

Sadly, this is a known bug with the router that TPLink can't seem to fix. I came here with the same issue I think last year or the year before, which is a year after I purchased the router and pretty much the same answers were given. 

I haven't read all the replies here (I'm rushing atm) but I've had minor success with turning off auto channel switching. This is either going to work to your advantage or detriment, based on how crowded your area is with Wifi. If you leave it on one channel and 20 or 40 Mhz width, I almost guarantee it will work for longer. It still crashes for me but less so. It used to go down every 2 weeks to a month but now it's more like a month at a time. My Archer 5400 also has an issue where it won't automatically pick up the new IP when my carrier switches my IP address, but that's not so bad because they don't do it very often.

So, the recommendation is to try 20mhz channel width and set it to ONE channel and leave it there. If 20mhz is slow or devices can't connect, go to 40mhz. If you can get a free wifi analytics app on your phone, you can see what channels are crowded and stay off of those. Worst case scenario, grab a cheap router or access point and bridge the 2.4 GHz wifi and use that and use the 5ghz from the Archer. I myself bought a cheap mesh setup which ironically, never goes down. The only reason I don't switch over completely is that it's AC1200.

Anyway, good luck. I'm done with TP Link, there's no real support. The answers are canned and from a script or something and the people who answer on here don't seem to know anything about the product. TP Link routers also have a 1 year warranty and according to one of the folks (who work there), there are no FW updates guaranteed after that so this bug will likely never be fixed.

Time to try another brand. I'm going to just invest in another mesh setup, albeit with more 5ghz bands, etc.

@Bjaerven same here, no more 2.4 GHz Network. it was working previously, and a few months ago i update firmware, and i don't know if it is related.

Hi,

I wanted to add my voice to the chorus: I lose 2.4GHz frequently. It used to happen every few weeks, now it fails after 2 hours. Support is unwilling or unable to help. This is not acceptable, doubly so considering how expensive this router is! I've been a repeat customer but this will be my last TP-Link product. 

@formercustomer 

Just a heads up. The only way I've found around this while keeping the router useful is to add back in my old router and use it for 2.4 Ghz. I've turned off the 2.4Ghz radio on the C5400 and it's been smooth sailing since. I think this has to do with either a bad batch of chipset or perhaps heating/thermal issues. I don't know but so far I haven't had issues with the router. I would still like to move to using ONE router vs. three (lol) but at least now I can say that it's not been a complete waste of money. 

Good Luck!

Same thing here.