This is my experience on MSFS2020 too.
@RulingPen63350 can you solve your issue by scrolling down a few extra times to make sure you’re right at the bottom?
On both msfs20 and 24 i always scroll all the way down (and more) but it won’t show up new messages automatically… thanks for the replies guys
This is one of those “fornever” bugs…
3 years later - it’s still a problem
As soon as you close the ATC window and open again it will scroll all the way to top (start) making it useless again..
Well i guess i should be thankfull to Asobo as its saving me the cost of MSFS2024.. i wont pay a cent again for broken products they dont give a ■■■■ about and wont fix even basic problems for over 3 years and counting.. why should i?
Something changed. I’m running the latest 2024 beta (as of today) and the windows scrolls mostly to the bottom. A very small amount of text is sometimes cut off on the bottom, but it is a lot better than it was!
Now the text will disappear and reappear as new messages come in. I think it’s a little better because I can still keep up with the flow, but there are still some annoyances. It’s an improvement, Asobo!
1 year later
4 years and a half after reporting the issue:
NOT FIXED
It’s fixed on 2024.. 
It is? Last time I used it, which admittedly was a couple months or so back, it was still acting up.
I thinks yes, since SU4 or 5 I’m not seeing this bug anymore, wich was really annoying to me before
Apparently it was in FS2024 SU3: