Found this old thread. Never know that this issue happening since last year.

My Maxis line having same issue since early this year, and until now the same problem still exist. Whenever connected to 4G+, most of the time can't load data at all. Already made complain few times but never get resolved.

Previously I always switched to 3G then only can use the Internet. Now 3G going to shutdown soon, so... no choice but I have to port out very soon since my contract already ended this month. Very disappointed with Maxis now.