Hey everyone, I may be late to the party here but I'm also having the same issue.

Funny enough, earlier this year I was living in a different apartment, it has unifi and the SocialClub service works just fine and I can play GTA 5 no problems. I moved to a different apartment much recently, although it's not far from my previous one, also has unifi. But it's when I've moved to this new place is where I'm having problems.
Sometimes I was able to log into SocialClub and my GTA 5 on PC, most of the time though, nothing.

Since I'm living in one of those college apartments, obviously the wifi isn't under my control, so I can't simply complain to TM about it. So the most I can do is use VPN, which pretty much renders GTA Online unplayable. (Most free VPN's are pretty limited on where you can connect to. I tried one of the VPN services, the trial period allows me to connect to Singapore which runs fine, but I no longer have that option after the trial ended.)

I was able to access the site and log into the game when I run through mobile hotspot no problem(I'm using Celcom).
But obviously I'm not that stupid to waste my data just to play a game that I can't access through my apartment's wifi.

What about Maxis Fibre users? If I'm not mistaken, some Maxis Fibre lines will share the same fibre line with TM Unifi(Not sure if that has anything to do with the problem or not.)

I was able to log into GTA Online and Social Club again.

My current IP starts with a 124.