The SD version of these 3 channels has been ceased for
Astro viewers, which are Astro Xiao Tai Yang (344), Astro AEC (346) and CCTV 4 (375).
If you are an
Astro subscriber, and you tune to CH344/346/375 right now, you should be seeing this
closing slide:

Source: One of netizen's comment on Astro Facebook page
If you are an
Njoi viewer, and you tune to CH344/346/375 right now,
you will still be able to watch the 3 channels as per usual, NOT the closing slide like what Astro subscribers gets to see now (refer photo above).
Note: The respective HD versions of the 3 channels (CH304, 306, 335) still appears as "This channel is not included in your subscription..." for Njoi viewers. Astro and Njoi viewers are seeing different thing on the same channel number? How? As you guys know:
- Channel List (Bouquet ID) for Astro subscribers and Njoi viewers are different (that's why you see some channels appears "missing" on Njoi compared to Astro). So to make it easier to understand, just assume there is at least 2 different versions of channel list, one is for
Astro subscribers, another is
Njoi viewers.
- Your Astro box will refresh the "channel list file" (Bouquet ID) regularly, so that whenever Astro make changes to the channel list (add or remove channels), the channel list shown on your Astro box will stay as up-to-date as possible.
So what happens now technically is, the broadcasts of the 3 SD channels mentioned is
still going on like normal, and aren't interrupted at all. They are still on the same respective Measat 3 transponder/SID/PIDs like previously. Nothing is changed there.
So I realise what the Astro tech guys did to its latest "channel list file (Bouquet ID)" that applies to all Astro subscribers that tunes to CH344/346/375 is, they
programmed it to redirect to
different transponder frequency/SID/PIDs that shows you the closing slide (as shown on picture above)
INSTEAD of the usual Astro XTY, AEC and CCTV 4 SD broadcasts like what Njoi viewers gets to see now.
In a more layman term is, let's say you're an Astro subscriber, you tune to CH344/346/375, so the tech guys "instruct" your Astro box to go to another TV channel on a different satellite frequency that shows the
closing slide (refer photo above),
rather than continue letting you watch the usual TV broadcasts of Astro XTY, AEC and CCTV 4 SD channels like what Njoi viewers gets to see now. So far get what I mean?
The advantage of them doing this, is to avoid the closing slide "suddenly appears" on your screen, where you're still in the middle of watching the 3 SD channels as the transition takes place on 15 March 2021 at 12:01am.
If you are an Astro subscriber, and if your Astro box have not "auto refresh" its channel list file due to whatever reasons (e.g. your Astro box still remain on CH344/346/375 and you didn't change to other channels, or
never put to standby mode or
never reboot), you will still be able to watch the SD version of Astro XTY, AEC and CCTV 4 as per usual (because you don't give chance for it to update channel list

)
Later once the Astro box auto refreshes the channel list when it gets the chance (i.e. you're not watching the particular channel, or put it to standby mode or you reboot the Astro box), then the CH344/346/375 will then appear as
closing slide.
I have to say, Astro broadcast tech guys is genius la...

I can see that they are trying very best to make the transition as smooth as possible, and as "less disruptive" as possible.
But well, some people just got no chill..... People out there are clueless and not properly informed about this transition

Imagine they've already memorised the SD channel numbers, now suddenly they're forced to memorise the HD channels numbers...

never know that such legacy 30 year old DTH technology support the "redirect" feature