Did more tests and getting the same results with this one, when connected to the TL-SG3452X on a gigabit port, I can only achieve up to approx. 300Mbps to the internet, but no issues when connected to the TL-SG3210XHP-M2 switch.

Here is my setup...

ISP Modem in bridged mode > OPNSense Firewall > TL-SG3210XHP-M2 (connected to OPNSense via 10Gpbs port) > TL-SG3452X (connected to TL-SG3210XHP-M2 switch via 10Gbps DAC cable):

- I have 1.5Gbps cable internet service, connected to a 2.5Gbps NIC card in my OPNSense server - WAN port

- I have a 10Gbps NIC card in my OPNSense server connected to the TL-SG3210XHP-M2 switch on one of the 10Gbps ports - LAN

- I have a 10Gpbs DAC cable connecting my TL-SG3210XHP-32 switch to the TL-SG3452X switch using the 10Gbps ports

- The 10Gbps ports are all showing connected as 10 Gbps Full Duplex

On my personal computer:

- I have a 2.5Gpbs NIC card

- When I connect to the TL-SG3210XHP-M2 switch (wired), I get full internet speeds (1,883Mbps down/54.7Mbps up) no issues here

- When I connect to the TL-SG3452X switch (wired), the maximum speed I can get is less than 300Mbps down/up is the same)

I understand that when I am connecting to the TL-SG3452X switch with my 2.5Gbps card it will only go as fast as 1Gbps on this switch, but why are the internet speeds limited to under 300Mpbs?  And it doesn't matter which of the 4 - 10Gpbs ports I connect to between the switches it is the same result (and I have tried multiple DAC cables).

If I connect the two switches just using a regular CAT6A cable (so limited to 1Gpbs between the switches), I can get almost full 1Gpbs from my computer (900Kbps).  What is causing the slowness on the 10Gpbs ports?

I think I may end up returning this swtich to Amazon, I still have a few days left unless someone from TP-Link can help.