Upstream Max Attainable Rate is 0

Personally I would not trust an att gateway's WiFi to do anything like what you're depending on.  BTDT.   I suffered miserably for a long time with dropped calls. That dog (wifi) don't hunt.  Buy you own solution.   I have no reason to believe the WiFi 6 implementation in the BGW320 is any better but have no direct experience with that device and it's likely what you'll get when having fiber installed.  I do have extensive experience with all prior gateways.  The good news is with a proper WiFi system in place, Att internet is generally reliable.

About the graph you posted, I'd factory reset the gateway.  If you still see bogus reporting, call it in.  I would make a fuss about your dependence on reliable wifi. Things to expect are getting a replacement gateway for starters.  But unless you have an actual line problem, the factory reset should clear things up.  Any testing you do should first be done after the reset and with only one hardwired device connected to the gateway to prove to yourself the internet connection is solid.  This also validates Att's obligation to you for service.   Everything else inside the residence is on you.  Good luck. 

I don't see any massive errors, looks like clean balanced sync all around. From your pic it appears you have 50M download but 5M upload. 5M upload is bare minimum for decent consistent teleconferencing, with everything else running on top of that it is going to struggle. Also the zero max upload (I believe) indicates that you are on an "F card" in the main box -- nothing wrong with that per se, its just that F cards do not output certain data on upload stats. 

If you can't wait for fiber to fix everything then check the site or call in to try upgrading the speed profile from a 50x5 to a 50x10, or even a 75x20. This won't be an option if there are only F cards available in your main box, but it doesn't hurt to check.

Agree with Shillelagh, certain line cards in the VRAD do not report the information back to the Gateway for it to be able to display, including the max upstream sync and the upstream error counts.  Your actual sync rate is known to the gateway and displayed, so you're provisioned at 55/6 and you have a good bit of excess capacity (which is good).  Your Signal to Noise margin is fine your attenuation shows that you're a fair distance from the VRAD (3000' maybe) but that's not a problem.

The AT&T do-not-exceed standard for FEC errors is 100 per minute, so you seem to have quite a way to go before that happens.  

F card… bonded pair

profile is 55/6 which is for internet 45

This was offered before the IBPP 50/10 which requires a K or N card.

Some VRAD only have F cards, (4) cards to a shelf.

You would need to call to see if faster speeds are available which would require a new installation appointment for double port swap. 

Even though I don't know all the jargon, all your answers have helped me to understand the situation.  I was hoping there was some kind of configuration fix, but now I see I probably have the "F cards".  @Shillelagh , I mentioned my screen shot was shortly after a restart, overnight those FEC numbers are 902 and 5026, respectively, not sure if this would be related to my reported issues.

I'll try hardwire to rule out the wifi.  I haven't done it yet, because it's inconvenient and it works so well for everything else.  Any thoughts, aside from wifi signal strength, around why internet just drops out of sight intermittently for 30 seconds, usually while I'm on a call?

They dug up the yards in November, so we'll see how long it takes to set up the fiber.  In the meantime, I'll steel myself up for "the call" starting with "please restart the gateway" and go from there.

902 and 5026 FEC "overnight" (assuming an 8 hour night) are well within norms.  

Any thoughts, aside from wifi signal strength, around why internet just drops out of sight intermittently for 30 seconds

You really need to determine if you're losing the connection to the Internet from the Gateway to the AT&T Network, or just losing your connection to your Gateway via Wi-Fi.  Different problems, different solutions.  If you don't lock your Gateway at a fixed channel, it can decide to change channels to avoid interference (real or imagined) on that channel.  When that happens, your client has to chase it to the new channel, and that might take 30 seconds (or longer) to resolve.

Max allowed FEC at 100 per minute, 6000 per hour, 144000 in 24 hours.

Overnight, assuming 8 hours would be 48,000 FEC or less… reporting 900 and 5000 overnight.

I suspect more gateway changing channel especially if close living quarters such as apartment, condo complexes… could also be other nearby device(s) creating interference. 

edit … may want to try an app like NetSpot to determine wireless survey…

https://www.netspotapp.com/

@dtv4me64 

If you’re sure you’re getting fiber (I have no idea how that’s known unless you see visible work being performed), then Att would have zero motivation to put newer cards in the VRAD.  Either way they need to give you acceptable service to the gateway.  

But, and this is important, the WiFi is not reliable in any access mode be it copper or fiber.  No configuration changes, nothing, will help.   It will be easier to see this once you’re satisfied the connection to the gateway is solid.

FWIW, I hated the F cards and was glad to get off them.