I came across the same issue on several MT devices.
What MT device are you using?
On my phone I get 46 down and 47 up on speedtest.
You mean phone directly to the provider or wifi connected to Mikrotik?
The reason that I am asking is because I repeated the following tests with several MT devices.
Mikrotik -- Cable -- PC -----> Slow Upload (Chrome, Firefox, windows application, command line all OOKLA speedtest)
Mikrotik Wifi -- PC ------> Slow Upload (Chrome, Firefox, windows application, command line all OOKLA speedtest)
Mikrotik Wifi -- Mobile phone ------> Fast upload (OOKLA Speedtest , nPerf)
At this point I thought something was related to the wifi or cable connection
Mikrotik -- Cable -- Access point -- PC ------> Slow Upload (Chrome, Firefox, windows application, command line all OOKLA speedtest)
Mikrotik -- Cable -- Access point -- Mobile phone ------> Fast Upload (OOKLA Speedtest, nPerf)
For all the cases which resulted in slow upload speed, when I used nPerf, PC upload was similar to mobile phone.
I noticed similar results with other mobile routers and services, so concluded that the problem is somehow OOKLA speedtest on PC related.