Just arrived in Malaysia and the process was very smooth. Flew United SFO-NRT and then ANA NRT-KUL.

United check-in staff checked our vaccination card, insurance documents, test results and verified we had the app installed. So far so good.

Transfer at Narita was a little disorganized for being Japan. Everyone connecting with ANA had to line up at a single counter to check documents. This process was very slow and inefficient. Once our turn they wanted to make sure the MySJ app traveller card showed "Pre-departure test: Submitted". They also wanted proof of onward journey since we had a one-way ticket to Malaysia.

Arrival at KUL was very efficient. Passport control as usual except they wanted to see the traveller card, that was it.

Once out, we headed up to the 5th floor passed the L check-in counter for the 24hr arrival testing station. No queue so we had are test results within about 30 minutes.

It seems the standard practice here is that you use your MySJ to check-in at places for contact tracing. We had to do that when we arrived at our hotel.
I was expecting chaos but it turned out to be very smooth.