@Michael_Night 

A couple of things to check.  Make sure your laptop network device drivers are up to date.  Also, try using different ethernet cable to see if that makes a difference.  Even if you are using the same cables that you connected to the modem with, I would still try different Cat 5e / 6 cables to rule it out.  I have seen failing/cheap cables work well with one device, and not so good with others.

You will see a little network overhead when additional devices are introduced bit not what you mentioned.  I suspect you are only negotiating a 100Mbs connection with the router and that could the cables.  On Windows 10, to see what ethernet speed you have negotiated with the router:

Left click on network icon in task bar by clock

Click on your ethernet connection (should say connected)

In the Settings winodw that opens, click on the ehternet connection that says connected

Look at link speed and verify 1000/1000

If it is 100/100, you have a problem negotiating the 1Gbps speeds due to old hardware (laptops network adapters), or cheap/degraded cables.  

Let me know what you find and good luck.

  @pcuttle Thanks for your reply. Please see below:

Make sure your laptop network device drivers are up to date.
Windows drivers, firmware all up to date. I tried to update network driver from device manager and that is all good.

...try using different ethernet cable...

I have 5e and 6 to try and that also looks good. I prefer using Cat6

I suspect you are only negotiating a 100Mbs connection with the router and that could the cables.

I have checked that out too and 1GB is detected.

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After some more testing, the issue is the upload speed. I should be at around 150Mbps rather than about 25Mbps. There is no issue when connected wirelessly. Here's the setup:

-The main office router is AXE75 (connected to switch)
-I use the Archer A10 connected to this network as it needs its own intranet. This router is dynamic and has its own IP Address so there is no conflict.

I suspect this may be the AXE75 detecting A10 and reducing its upload speed? If so, what settings would I be looking for?

I also did a factory reset with no improvement.

This is a very familiar issue when using the A10 at different venues. I have others report about something similar and all I can think is that its the venues network preventing high speed uploading. QOS is off on the A10 and I can check AXE75. I believe by default QOS should be off.

Thanks for reading! Much appreciated!

  @Michael_Night 

Have you considered using a guest WiFI network configured on the AX75, segregated from main network?  Do you have/need wired connections to A10 that need to be on a separate network?

 Thanks so much for your time @pcuttle 

I have run a bunch of tests and it just seems that both TP link routers connected together for some reason will keep that max upload speed of about 20-25Mbps from about 150Mbps.

Its a special setup for events at venues. Typically the venue provides a hardline conection to the A10's internet port. The A10 connects to a switch (cat6) that's connected to about 10 or so devices and that's it. I have run events where speed tests are almost 1000Mbps up and down. Wifi is only used for a few devices.

QOS is off on the A10 and the AX75 does not have one unless you have the home security app from what I understand. I did try to make sure both modems nagociated 1000Mbps full duplex and that did not seem to work. I also disabled 1 mesh on the AX75 since we do not have the extender.

Connecting AX75 directly to the laptop will have no issues. Connecting the AX75 --->A10 (WAN)--->laptop (LAN) has the upload limit issue. The A10 has its own gateway and nothing else is modified.

I did try a selection of CAT6 cables and they all check out good.

I'm not sure what else I can try.