A critical issue with the wireless upload speeds on the EasyMesh wired network with one main BE550 and a second BE550, specifically from the satellite Archer BE550 unit, is occurring. The problem started after installing the second BE550 router as a satellite in the mesh system.
 

Network Configuration:

• Internet Connection: 1Gbps symmetrical fiber via Hyperoptic, connected to the main BE550 router via ONT.
• Backhaul: The main and satellite BE550 are connected via a 50ft CAT5e Ethernet cable. EasyMesh settings confirm a wired backhaul connection with a reported speed of 2500Mbps. Although I note Cat5e is not technically rated for 2.5Gbps, it had previously worked at 2.5Gbps before I installed the second router, so I can confirm the cable is not the issue as will be described later too.
• Client Association: Wireless clients (MacBook Pro M3 Max, mobile phones, PC) are correctly associated with the nearest satellite BE550 in the office or main router when testing (I've confirmed in the tether app and via the web UI with connected clients showing which router they are connected to) 

Observed Performance (with satellite unit):

• Wired Macbook Pro M3 Max with USB C dongle ethernet (connected to satellite): Full gigabit symmetrical speeds (approx. 900Mbps download / 900Mbps upload). This test confirms the satellite router's hardware and the Ethernet backhaul are capable of full speed Hyperoptic fiber.
• Anomaly in testing wired on the PC: Upon testing the PC wired (using the exact same ethernet cable that was connected to Macbook) I get the full 900Mbps download but only get 600Mbps upload. (I've not changed the cable, and it did previously work as I had the main router in the office on the same desk as the PC, but now the satellite router sits there and the main router sits between the ONT and the 50ft cat5e cable going to the satellite router.
• Wireless Clients (MacBook, phones, wireless PC): Asymmetric speeds, with significantly degraded upload performance.
  • Download: Approximately 900Mbps.
  • Upload: Only around 200–250Mbps.
  • This low wireless upload speed affects both the 5GHz and 6GHz bands equally. Although the PC when wireless has varied results, sometimes the download is only 400Mbps and the upload is 700Mbps.

Testing and Troubleshooting:

• Cable Integrity: An Ethernet cable was tested by connecting a MacBook directly to the satellite router, which confirmed full speeds (900/900Mbps) wired (only on Macbook).
• Individual Router Performance: My PC was connected directly via Ethernet to the main router before purchasing the second router. Full gigabit speeds were confirmed (900/900Mbps) when testing either just the main router or just the second router (not plugged in at the same time or in easymesh mode) 
• EasyMesh Reset: A factory reset was performed on the satellite unit, and it was removed from the mesh via the main router's interface, followed by a clean re-pairing. The issue persisted.
• Disabled Features: Flow Control and QoS were disabled, with no effect on the upload speed.
• Band Specificity: Both 5GHz and 6GHz bands were tested, confirming the slow upload speed is consistent across both, indicating it's not a band-specific issue.
   

Conclusion:

The symptoms suggest a bug in the EasyMesh firmware. Despite the fast, wired backhaul connection to the MacBook, the mesh system appears to be improperly routing wireless upload traffic, possibly defaulting to a slow wireless backhaul path. Consistent download performance suggests the wired backhaul is used for that, but the slow wireless upload indicates a processing or routing bottleneck introduced by the mesh software. It's also possible that because a CAT5E cable is being used the routers could be incorrectly reporting the speed as 2500Mbps between them when It should be 1000Mbps, or at least I should ahve the option to choose that. 

TL;DR:

In a two times Archer BE550 v1 EasyMesh setup with wired backhaul, wireless upload speeds from the satellite unit are capped at 200-250Mbps (despite 900Mbps downloads), while wired tests show full gigabit capability from one device but not another. Troubleshooting (resets, disabled features) failed; suspect firmware bug in traffic routing. Seeking fix or update.