I'm a Streamyx user as well,  it disconnect frequently at night with the phone line(copper) down as well. Since the internet speed depend a lot on your phone line, cutting the phone signal is same as cutting your internet connection. However the internet and phone line working flawlessly during day time mean someone/program is systematically reduce/cutting the line's signal at night. Why? Because they can milk money from you if you report your problem and they'll eventually send someone so call "contractor" to collect money on the spot(without receipt, which is illegal!). They will tell you they are not doing it for Telecom malaysia berhad while they are wearing Telekom's worker cloth, using Telekom's testing device and driving Telekom's car, then they'll tell you how much they will charge you after the service is complete. They will look for what ever service they think they can charge you for RM100-200.
new copper line wiring or modem(which is B*U*L*L*S*H*I*T in my opinion). It doesn't make sense, if the copper line wire is spoil, it should be not working at all. Why is it working during the day and not the night?  those contractor that tell you to change the wiring obviously is bull-shiting you.

I have been charged for 2 times before for installing new wiring service(copper line)RM 150 each. Telekom live chat people told me that any service they provided on site will be charge to the next month bill, however the so call contractor collect money without printing receipt is just look suspicious to me. Each time i installed new wiring, it work for several months to 1 year and finally the problem will start to come back. it is either a group of people inside Telecom Malaysia Berhad is doing some dirty under the table stuff or they secretly launching a new method of anti-piracy(reduce your total time of internet access by cutting it off during night, which is a lot of p2p torrent activities time). In the worst case, both is true.

total 21 million internet users(2016) 
if 10% is targeted and milked:  RM 2,100,000 X RM 150 = RM 315,000,000
with this much money involve, i expect a lot of corrupted peoples inside Telecom.
So now you know why your unifi/streamyx are not working during night!

DO NOT pay the contractor without receipt, you should insist on pay via the next month bill. If you pay them, you are encourage them to shut off your internet connection during night. They do not dare to shut off your internet connection during the day for a reason, They can't do it because a lot of people watching. So they do it at night where a lot of colleague is went home. Without any profit, they won't bother to cut off your internet line during night anymore.

The IRB is our best friend, those under table deal is evading tax and GST, if you manage to get evidences and report it to them, they will be very happy to investigate Telecom, since they want a piece of the cake as well(Yummy).

I have a solution for all of you, each of you should take a picture of the employees card of the contractor that visit your house, do the same for his face as well. Record down the whole conversation if possible. You should insist pay via the next month bill or asking for a receipt. If they fail to do both(take money from you without printing a receipt), reported it to MCMC and IRB immediately to solve all of your problem!