@Leandro011 

For the slow speed issue you encountered with the Archer AX10, please help verify some details, and we will try to fix it together:
1. May I know who is your ISP? When you connect a computer directly to the modem, what is the download speed? How about you connect the same computer to the AX10 with the Ethernet cable?
2. Does the speed slow down after you upgrade the router firmware? Or this issue just happen without any change in the network?
3. Do you enable any QoS setting on the AX10? Kindly show me the QoS setting page, ensure the QoS settings on the router is on Standard mode, and no high priority devices, if the speed on the page doesn't display correctly, change it to Set Manually and type in the correct bandwidth provided by your ISP. Or simply reset the AX10 and reconfigure it from scratch, leave all settings by default and test the speed again.
4. What kind of devices are connected to the 2.4GHz wireless and what is connected to the 5GHz? How about the link speed on them when the speed drops? If it is a computer, you may check it like below:
https://www.tp-link.com/support/faq/2265/
Note: If the link speed is not as good as expected, please try with another computer with a more powerful wireless adapter. BTW, tell us the model number of that wireless adapter that runs on your computer.