Sometimes, those contractors are just finding the easy way out.

If the leak is severe, the wall has to be "opened" up partially to find the source, which will incur more money and time to fix the actual issue.

If multiple waterproofing failed to fix it, most likely have to part by part, break up the wall to find the issue.

My toilet had an embedded pipe which started to leak. Had to break open the wall, fix the pipe, apply waterproofing and seal up the wall, repaint. Tedious work.

The water seems to be coming from the soil to be honest. Your new front of the wall picture shows that the bottom part of the wall, even from the outside, has wavy pattern.

The extended black tile section may or may not help if the soil is wet due to long term exposure to water.

When my contractor fix my upper level toilet which is leaking water to the lower level, he used some thick waterproofing kinda cement as base.

You are right, I think due to the age of the house the ground water has come up or something. After some reading we have figured it's an issue called "rising damp" and it's quite a complex thing to solve. Been contacting multiple local leak/waterproofing "experts" but it's an exercise in futility. Hope to find an actual expert that can go with chemical solution rather than a renovation route, as we have just come out of a fully fledged reno. It's obviously very frustrating that this wasn't dealt with more thoroughly during the renovation, and the contractor only painted some dodgy waterproofing solution to the wall as "a favour" to me.

Well if anybody knows any contact that understands Rising Damp please send them my way thank you.

Just be careful of scammers.

It is a shame that most house reno/contractors in Malaysia are not very skilled.