I haven't noticed this issue until today as I was using my Onn, on my 5GHZ.
For some reason, when I connect to either of my 2.4GHZ APs with the on, it's claiming speeds like 2mbit-8mbit out of my 100mbit Internet.
5GHZ as expected gives at least 85-93mbit.
What's weird is, when I speed test both 2.4's with my phone, they give at least 20-50mbit each.
Mine was getting horrible 5GHz WiFi a few days ago -- I think one of my other devices, possibly my Bluetooth audio transmitter, was interfering with it from where I had it placed. I moved it away from that spot and it's working fine again.