Intermittent Internet Service?

Environmental problems such as overheating can definitely cause you issues.  Unstable power can likewise cause problems.  Be sure that your Gateway is where air can freely circulate around it and the ambient temperature is within the environmental specs posted for it, don't lock it in a small cabinet with no airflow.  A fan isn't a horrible idea, and is a decent use for the USB port.

Looking at the manual for the bgw210 gateway:

The BGW210-700 Broadband Gateway is intended for use in a consumer's home. Position the
device in an upright vertical position located where ambient temperatures remain within a
range of 32°- 107°F (0°- 41.7°C). The BGW210-700 Broadband Gateway should not be used in
locations exposed to outside heat radiation or where it is subject to trapping of its own heat.
The product should have at least two inches of clearance on all sides except the bottom when
properly installed and should not be placed inside tightly enclosed spaces unless proper
ventilation is provided.

Given those requirements 77 degrees really shouldn't matter.  My bet would be the gateways you've received are bad/damaged "refurbishment"(in at&t language that just means used).  While a fan might help extend it's life as lower temps are almost always helpful to electronics, I'd bet your current one doesn't last long.  It's probably got a bad solder joint or capacitor or something, and the slight cooling helps keep it just barely connected.  Or a bad power supply (make sure you swap power supplies when you replace gateway).

At&t buys the cheapest equipment they possible can and then does a terrible job refurbishing it.  It's not uncommon to get multiple bad units before finally getting a descent one that'll last.  I would also definitely be aware if there is any other equipment near by putting out heat, tv's, 3rd party router, dvr, stbs, even just power transformers plugged in nearby.  An electronics cabinet without probably airflow can get 100's of degrees hot and melt things.  but a 77 degree house with proper airflow? that should NOT cause problems.

Thanks for your comment. Not sure about inferior AT&T equipment.  The original modem/router AT&T installed worked great for at least two years without a problem.  After AT&T installed the new modem/router I continued to experience the same issue.

My modem/router is located in a well ventilated area and not located near a heat source.  In my case, the TWO degree room temperature change did make a difference.

While waiting the two days for the cooling fan, I continued to test the system, lowering and raising the room temperature, same outcome every time.

Putting all the technical jargon aside, either lowering the room temperature or using a cooling fan fixed the intermittent internet service I was experiencing.  

@trevor7435 yea that's normal.  New well built routers should last forever or at least like 5-10 years since there aren't any moving parts.  If you look at back of router you can usually find a manufacture date and refurbished date on box they send it in.  

All the technical jargon aside if it was me I'd keep asking for replacements until they sent a gateway that worked on its own without me babying it.  But if you don't mind losing your internet unexpectedly just keep it as is until the current one breaks.  

Was your old gateway the same model # as new one? What model is new one? Bgw210? 

Madmax988, the old gateway was a different model.  The  new gateway the tech installed is as you stated Bgw210-700, mfg 9/6/2021).  

I have had continuous internet service for a month now.  That’s with the cooling fan.  

Getting a new gateway is easier said than done.  AT&T didn’t replace my gateway until the 4th tech visit to my home.  After spending MANY frustrating hours waiting and dealing with AT&T tech support, I’m just not going to put myself through that again when things are working well.

If or when I contact AT&T customer service again, it will be to cancel service.  We now have Google Fiber in our area.  If I have internet trouble again, I may give Google Fiber a try.

Thank you for your input.  I appreciate it very much.

If I had google fiber available I would flee from att as fast as possible.  Although I'm guessing you are at least on att fiber. And not 50mbps copper like me lol.