It seems that speedtest is consuming too much performance.
Which speedtest client are you using?
- speedtest-cli in python from opkg?
- speedtest in C++ from Ookla website?
If it is the former, it may be that updates to python or speedtest-cli have caused them to consume more performance.
Please try the official version from Ookla.
wget https://install.speedtest.net/app/cli/ookla-speedtest-1.2.0-linux-aarch64.tgz
tar -xvzf ookla-speedtest-1.2.0-linux-aarch64.tgz
chmod +x speedtest
./speedtest