Issues with latency and jitter

If your main source of upload is limited to 6 Mbps up, then that should keep the pipe open, but that's not what it looks like.  I would keep a PING -T of the IP address of hop 2 (from your tracert) going all the time and glance at it from time to time. I'd bet when that goes to 300+ ms, you'll be having a problem and see if you're okay when it isn't.

If that turns out to be a solid indicator, then we can look more at the upload.  If that's not a solid indicator, then we can look elsewhere.

Assuming you don't have fiber...

Go the the gateway at http://192.168.1.254/ 

Click on the Broadband tab, and look for the tables that include information like sync rates, attenuation, noise margin, and error count.  Also the in and out byte counts and uptime would be useful.  Make screenshots of all these things and post in replies to this thread.

When you say VOIP, do you mean AT&T's VOIP (AT&T Phone) or something else?

Also, what types of other things do you use your Internet connection for while you're experiencing these issues.  Especially things that send data to the Internet. For example: online backups (including phones), P2P networks.

Yeah definitely not fiber haha, I wish. The only service we have is AT&T Internet 50, by voip I mean Zoom meetings, voice chats like discord, etc. Anecdotally it feels like the connection drops out occasionally for a second and needs to reconnect, but I don't know what data would show that. We notice the most issues for Zoom meetings and uploading/downloading large files (they often fail and need to be restarted) since we both work from home. And a ton of latency and jitter issues during online gaming as well... not the most important measure but definitely the most noticeable.

I can't tell how long your Gateway had been booted when this snapshot was taken (no uptime) but your line looks pretty decent.  I'm a little concerned that your upstream sync rate is higher than your max attainable.  Your downstream rate is well within the maximum sync.  Your attenuation is okay, your margin looks okay, and (unless the gateway had been up less than 15 minutes) even your FECs look fine.

Your tracert in the first post showed a 200+ ms latency on the first hop.  That can almost always be attributed to overloaded upstream, i.e. you're sending data at the maximum upstream rate.  This, in turn, means that (since the Gateway has no Internet QoS to speak of), other traffic has to get in the queue of all that other traffic that's going out and slows everything down.

Thus, I did see what I expected in the Transmit Bytes and Receive Bytes.  Your upload is 4 times your download, which is atypical for most customers, but very typical of those with overloaded upstream.  It looks like your Gateway was booted less than 24 hours before the screenshot (because the 80 Unavailable Seconds is likely at boot time and is in the Current Day).  Yet during whatever time that was, you sent 1.9 GB to the Internet (and only downloaded 500 MB).  At an upstream sync rate of 10 Mbps, that's 26 minutes of full utilization.  Even full video Zoom calls shouldn't be sending that much data to the Internet.  Normal file uploads don't typically send that much data.

That is likely not your only issue, but it is something that is causing jitter and high latency whenever those transfers are going on.  To address that would mean either figuring out how to limit the upstream usage of whatever is doing that, or inserting a router into your network that can implement QoS and make it possible for other traffic to work around the bottleneck.

If you notice a pause in your connection, and then it catches up... that could be an affect of the above, or it could be a Wi-Fi interference issue or the Wi-Fi changing channels to avoid interference.  But that would apply to Wi-Fi... are your devices wired or Wi-Fi?

The pause could also be an effect of DHCP lease renewal.  You might consider extending your lease time above the default 10 minutes.

Yeah, I had restarted the broadband just a few hours earlier. We do have a lot of upload because my wife is a video editor and downloads then edits then uploads videos during work hours. I do have a Unifi AP set up that she uses for the wifi but it does have QoS enabled limiting to 6Mbps upload there should be some room to work with. But we do get issues whether we are uploading at the time or not. Also just to note, we have 1 TB/mo soft data cap that we never pass, usually we do 600-800 GB. She only uses the wifi but I notice the connection pauses on my computer as well on ethernet which is going directly to the gateway.

For the last day or so our service was working great, with 20-30ms latency and no jitter. But then it started having issues again - I noticed the service paused and when it came back up I ran the following tests. This lasted about 15 minutes or so before returning to normal. Of course these kind of issues can happen periodically in any network but we do get them every few hours usually. We do live in a very dense area, our apartment complex has 4 buildings with about 150 units each building, so that may play a part of it.

I do very much appreciate the help by the way!

Turns out you were spot on about the upload! It ended up being two things, the QoS rule that I made seemed to have been unapplied to the devices from a controller update so the limit wasn't working, and then there was a dropbox app constantly syncing for some reason without doc changes. Fixed both of those and now our issues have dissapeared! Doesn't help my neighbors lol but thanks for the help Jeffer!

Maybe the neighbors also have dropbox sync issues. :)

I found out how badly a full upload pipe hurts performance when my daughter would bring her smartphone home from college.  Apparently it wouldn't treat the college's WLAN as Wi-Fi and it wouldn't upload pictures and videos to the cloud until it got on my network.  Then it took several hours to upload weeks worth of photos, videos, whatever.  It took me a bit to track it down to that phone.  Now I have a router that implements QoS and can also track and limit bandwidth on a per device basis, and she has her own Internet service.