@gbro
Hi,
In case the RE605X is currently located vertically right above the AX55, then try to move the RE605X to another position that is horizontally offset by some distance and check if that improves the speed a bit.
You could also play around with the adjustable antennas of the AX55. For example, adjust them in a 45° angle and then check if that gives some improvement. The way these pole antennas work is that the signal is emitted from the long sides of the antenna, while there are dead spots in the directions of the two tips of the antenna.
Besides the above, the AX55 is an AX3000-class router (signal rate of 2402 Mbps at 5 GHz), while the RE605X is only an AX1800-class device (signal rate of 1201 Mbps at 5 GHz).
Note: Don't confuse "signal rate" with practically achievable download speed.
So, if you were to upgrade the RE605X to an AX3000-class device, then you could expect to double the practically usable download speed.
If you want to get near 850 Mbps through a wireless extender on another floor, then both, the router and the extender would have to be replaced by higher spec'd devices.
By the way, does your AX55 provide information about the RE605X's link speeds within its "EasyMesh/OneMesh" menu? If yes, what numbers do you get?
