GS110EMX: 10G ports throttle uploads to 250-300 Mbps

I've been going back and forth with Netgear support for over a week about this and I'm honestly at a loss. I'm hoping someone here can tell me if I'm crazy or if what they're telling me doesn't make sense, because it really doesn't add up to me.

My Setup

• Switch: Netgear GS110EMX (firmware 1.0.2.8)
• Port 1: Internet uplink (1G, connected to router — standard fiber ISP)
• Port 9: Mac Pro via OWC Thunderbolt 4 to 10G Ethernet Adapter
• Port 10: Asustor AS6508T NAS (10G)
• Cables: Cat6A throughout

This is exactly why I bought this switch — two 10G ports for my computer and NAS, with everything else on the 1G ports. Pretty standard home prosumer setup.

The Problem

Internet uploads are throttled to about 250-300 Mbps when my computer is on a 10G port. Downloads are fine at 830-880 Mbps. When I move the same computer to a 1G port with the exact same cable, uploads jump to 708 Mbps. That's more than double the speed on a port that's supposedly 10x slower.

What I've Tested (at Netgear's request)

I ran every test their L3 support team asked for. Here are the results:

Internet Speed Tests (computer on 10G port 9):

Internet Speed Test — computer on 1G port (same cable, same everything):

iPerf3 between Mac and NAS (local, 10G ↔ 10G):

Local 10G performance is excellent. The ports, cables, and NIC all work fine.

What Netgear Says

After all this testing, support came back and told me:

1. This is "working as expected" and "within the design limitations of the switch"
2. The 10G ports are "intended to be used as uplinks" — not for client devices
3. A replacement would behave the same way
4. My configuration is "not the intended use case"

Why I'm Confused

I don't understand how any of this is "expected behavior." Specifically:

• How does a 1G port give me faster uploads than a 10G port? If the 1G uplink is the bottleneck, moving to a slower port should give me equal or worse speeds. Not more than double. Nobody has explained this.
• Why are only uploads affected? Downloads through the 10G port hit 865 Mbps — nearly saturating the 1G uplink. The traffic crosses the same 10G/1G speed boundary in both directions. Why would only one direction have "buffer overflow" problems?
• Flow Control made things WORSE. They asked me to enable it. It dropped uploads from 306 Mbps to 137 Mbps. How is that a fix?
• The product page says "No Network Bottlenecks thanks to the 2 10-Gigabit/Multi-Gigabit Uplinks." Now support says those ports are only meant to be uplinks and my setup is unsupported. The user manual literally shows 10G client devices connected to ports 9 and 10 in its network diagrams.
• This switch used to work. I used the exact same setup with fiber in Chicago for years with no issues. I only noticed the problem after switching to fiber here in LA recently. Something changed.

What I'm Asking

Has anyone else seen this? Am I wrong to think a managed switch should be able to handle 10G devices sending traffic through a 1G uplink without losing 70% of the uplink's capacity? I've seen a couple other threads about similar issues with the GS110EMX and I'm starting to think this is a known design flaw that Netgear just doesn't want to acknowledge.

At this point I just want to know if I should keep fighting for a replacement or just give up and buy a different switch.

Any insight would be really appreciated. I've spent way too many hours on this already.