Internet is nearly unusable (slow speeds, connection errors, etc.)

I have the double play package with up to 200 Mbps download speeds. This week, we had an outage for about an hour on Wednesday. When I checked the status of our connection, it said techs were in the neighborhood fixing the problem. We noticed our gateway reboot twice while the techs were working, and then we were finally able to get back online.

Since then, the internet has been nearly unusable. At some points, a speed test shows 2.12 Mbps down. Any site that has a lot of photos or videos doesn't load properly--it just shows white or gray boxes where the photos and videos should be. I can barely even connect to my email account to send a message. I rebooted the gateway several times, which didn't help. Support says they won't send anyone out due to COVID-19, so the agent sent me a new XFi gateway. It arrived today, I set it up, and the problem is no better.

When I installed the Xfi app, I noticed that it says 93 devices are connected to our gateway. I created a completely new network SSID rather than using the old one, but within 10 minutes of setting up the new gateway, it had 66 devices connected to it. Could this be causing the slow internet? If so, how do I prevent all these devices from connecting? We have a lot of devices, but we certainly don't have 60+. We have two iPhones, two laptops, two Kindles, a PS4, and a Roku stick (so 7 devices total).  The device list shows about a dozen Apple devices, multiple Samsung devices, multiple HTC devices, etc.