Hi oldbroad!
Give AT&T a call if you have not yet called
I had to call them yesterday because my internet speeds were not up to par. Using this
AT&T Official Internet Speedrun Test I was only pulling 200mbps instead of 800+ on the new computer hardwired. The automated system answered the phone. After locating our account it asked me to tell it what was wrong. I answered "internet speed". it ran a test on our system and found nothing wrong with it and then connected me to a representative. Two rings and I was talking to support. It turns out my "nic card" could be the culprit. The W10 was getting those high speeds but not the W11. I have to call Geek Squad today. AT&T has always been very helpful and quick in solving our issues. They might even be able to tell you it is the weather or outages
There are a few support numbers out there.
This is the number I used . Scroll down to the bottom, you will see the "Give us a call"
I was on the phone for 30 min with them running tests on the system and us narrowing it down
Anyhow give them a call. They have also upgraded their modems not too long ago, at least the fiber optics modems. Ask them about that. You could be due for a new modem