use vpn...
use unifi dlink router

my issue is....my father sometimes cant receive internet connection at certain specific time. example at 10pm suddenly no internet. it can goes to night. but my one still ok... although i receive some interuption.

so whats gone wrong. what things that vpn has kacau?

Are you using VPN for any specific purpose ie work server, security etc ??

VPN usually slows things down significantly for normal internet use, so try to switch it off when not necessary to use it

No. No longer use VPN now. But it seems it has reset a lot of setting in the router . Which i dunno how to set it back to normal

Right ....

Factory reset to default settings, then setup the router again for normal internet

VPN is good for bypassing blocking by TM.