Does throttling occur?

So I'm not a complainer. I have been genuinely happy with At&T U-Verse and Internet and have been a customer overall for going on 20+ years. I currently have their 1000 mbps package and when testing the speed on the gateway, it does indeed show 989 mbps. But like most of you, I work through WiFi. I use an iPad Pro and on good days my Ookla Speedtest app would show 300mbps consistently, even two rooms from the gateway. For the last week and a half, I'm showing just 18 mbps consistently. I also do online gaming via wifi on my gaming laptop in the evenings and now all I get is lag and stutter. It's towards the end of the month, but I've read articles where AT&T denies they are throttling me on fiber. I can see them doing that on cellular, but not fiber in the home. Has anyone else noticed this problem? Are there easy solutions, could it be the gateway hardware, or am I at the mercy of the alleged no-throttling? I've run every test imaginable and nothing works. to speed it up. I often have to turn on my phone's hotspot to get faster speeds than my home wifi.