Many other users have reported the same problem, so it does not seem to be an isolated case.
In my case, selecting different Speed Test servers in the WebUI does not resolve the issue.
I have also performed a full factory reset of the RUTX50, but the problem still persists.
What is interesting is that the Speed Test feature worked correctly when I first purchased the device, and the issue only appeared later.
This suggests that the problem is not related to our current configuration, as even a factory reset does not restore the original behavior.
There is also no difference depending on which Internet connection is used.
The issue occurs regardless of whether the router is using a WAN connection, SIM 1, or SIM 2.
My WAN Internet provider is Tele2.
SIM 1 is also using Tele2, while SIM 2 is using Telia.
The same Speed Test issue occurs with all three Internet sources, which suggests that the problem is not related to a specific ISP or connection type.
I look forward to your further investigation.