Malaysia and Singapore both have a long standing relationship with Taiwan, however they recently dropped the visa free privilege on the two countries. It is unclear why they’d remove Malaysia and Singapore, but Japan and South Korea were eligible for a 90 day visa.
According to a Singaporean news site, Taiwan has recently decided to open up their borders like how the rest of the world has done in the past few months. Other countries affected are, Russia, Israel, Chile, the Philippines, Dominican Republic, Thailand, Brunei and Nicaragua.
The Taiwanese representative mentioned that it was misunderstood that these countries’ residents were allowed to enter visa free to begin with. Those travelling to Taiwan still require to undergo the PCR test and a 3 day quarantine.