Anyone experience slow or unstable internet at night recently? I've been facing this problem for past few days.

im living in double storey house. unifi modem and router (2nd gen orange and white) is upstairs. i cant receive any coverage downstairs. however, i found out that the silver router without antenna (4th gen) has better coverage. i tried to call tm to change but they are saying that the silver router is unstable and has more issues. I would like to know if anyone using the silver router face any problem like disconnecting often.