Found this in Grabhitch's FB Group. Seems like the glitch is affecting drivers and riders.

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Dear Grab Team,

I refer to your recent implementation of number masking for GrabHitch rides. I’m presently writing in as a GrabHitch driver.

The recent masking of cellphone numbers has resulted in a plethora of failures for both Hitch Drivers and passengers. Please refer to the Singapore GrabHitch Community Page on FB to understand what is happening. My SMS text messages are being severely delayed and I’m also not receiving prompt confirmation for Hitch bookings. In addition, passengers are not ready for pickup because they aren’t receiving messages instantaneously, despite being sent ahead of time. Please bear in mind that GrabHitch is a service catered primarily to private car drivers travelling through a defined route. We are not obligated to spend wasted time waiting for passengers because of such problems. As cancellations will inevitably increase because of this unfortunate problem, it will cast a negative perspective of the GrabHitch service and ultimately of Grab in itself.

The second point is, the feedback I received from passengers is that, they are refusing to answer the masked phone numbers with the 31**-**** prefix because many of them have deemed this to be marketing or survey-related phone calls. It is obvious that GrabHitch isn’t your GrabCar on-demand service. The time of GrabHitch Drivers is extremely valuable and we cannot be compensated for lost time. You will lose your Drivers ultimately.

It is my genuine desire that Grab support reviews and escalates this feedback email, and reverts to the original arrangement of direct contact between the drivers and passengers for this social carpooling service to truly work as intended.