Your local router buffer fills up (measured upload is fast!

), then overflows, packets are dropped, the upload stalls, the buffer empties, and the process repeats.

A version of Android from 2 years ago is not likely to work well.

during the test using the operating system CPU meters.

If the PC is not IDLE before the test, or if the CPU usage gets over 50% DURING the test, then this could indicate a problem.

Restarting the browser or rebooting the PC may reveal the CPU use is runaway processes left over from earlier in your sessions.

general you can solve any issues with mobile speed measurements by simply setting the number of upload/download streams to 1/1, and then increasing it to find the best setting.

Having a CURRENT version of your mobile OS and browser is also a big help.

If the objective is to test the quality of your internet connection then you should disable any proxy servers.

In rare cases your ISP may impose a proxy server of some kind that you cannot disable.

If your PC uses one or more SSD (flash) disks, it could be 2 to 8 gigabit.

Only the fastest internet connections start to exceed the speed of a typical disk sub-system.

Because browsers typically download files and store them on disk the upper limit of this speed test is going to be limited by the fastest write speed of your PC disk drive.