Orbi RBR50 Why is speed so variable minute to minute?

Thanks for the information.  We know that although devices within the LAN can reach speeds determined by their individual capabilities, internet speed can never exceed what the Internet Service Provider supplies.  Thus...

• Two computers connected to gigabit Ethernet ports on the router can reach very close to full gigabit speed.  (Even Ethernet has overhead which reduces the maximum possible throughput.) I have measured over 900Mbps between two Windows computers.
• Devices connected with WiFi can reach speeds which depend on the capability of their WiFi adapters.  2.4G connections, for example, cannot reach nearly the maximum speed that 5G devices can.  The Orbi RBK53 system is a WiFi5 product, with 5G capable of 802.11ac speeds. (a maximum Link Speed of 833Mbps) As with Ethernet, there is overhead inherent in WiFi (a LOT of overhead).  My tablet, for example, reports a "speed" of 468Mbps, but achieves just under 300Mbps when I test it.
• A useful tool for measuring network speed is iPerf3 (free for Windows, Linux, Android at
  https://iperf.fr/iperf-download.php 

However, internet speed depends on the Internet Service Provider.  No matter how fast devices can connect to each other within the LAN, their internet speed depends on the ISP.  It would be useful to know what speed AT&T has guaranteed in your contract.

That said, speeds of 2-3 Mbps are insanely slow.  Something is seriously wrong.  When a phone reports being connected to the WiFi network at 833Mbps and the Orbi app is reporting over 200Mbps, this is not right.

What this sounds like is serious WiFi interference that is intermittent.

Most customers would start with a call to AT&T. "Is something going on with my Internet???"

Keep a log of the Orbi app reports for some period of time.