Same here. I tried reset wifi mobile and bluetooth, and thhe problem still occur. I have tried checking the internet speed on my laptop and iphone, they all work correctly. On my asus rog phone 2 the download speed only at around 10% which around 10Mbps. I have 150Mbps internet package. This just happen very recently, i think around this week.
Option that i have tried:
the standard resetting internet (unplug, calling provider, etc2.)
reset wifi mobile and bluetooth
restarting the phone
changing IP
limiting other wifi user bandwidth
Pray 😄