Textview won't scroll when using append - kotlin

Question

I'm trying to get a TextView/ScrollView in Kotlin to scroll to bottom after appending text.
Weird thing is, I have it working perfectly for 1 TextView, however, another (near identical) TextView doesn't work?
So after a while of struggling to find a difference, I finally found ... something ...
I was populating one of them:
textView = text
and the other
textView2.append ( text )
The one using append, would not scroll to bottom, nor would it show the shaded curve for "overScrollmode" (which is set to true).
Obviously, I was using append, because I'm adding a small amount of text, repeatedly.
The other textView, is an "all or nothing" replacement. (in reality, I don't want the latter to scroll down, I actually set it to scroll to 0,0 (top), however, I used it as a test to find this issue :) )
So why does a text view, when using append, not honor/scroll as a result ?
<androidx.cardview.widget.CardView
android:id="#+id/cvMoveHistory"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_margin="5dp"
app:cardBackgroundColor="#025D68"
app:cardCornerRadius="8dp"
app:layout_constraintBottom_toTopOf="#id/cvMoveHint"
app:layout_constraintEnd_toStartOf="#+id/linearLayoutBoardButtons"
app:layout_constraintStart_toEndOf="#+id/frLayGameBoard"
app:layout_constraintTop_toTopOf="parent">
<ScrollView
android:id="#+id/svMoveHistory"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginStart="5dp"
android:layout_marginTop="5dp"
android:layout_marginEnd="5dp"
android:layout_marginBottom="5dp"
android:fillViewport="true">
<TextView
android:id="#+id/moveHistory"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#939393"
android:fontFamily="monospace"
android:padding="4dp"
android:scrollbars="vertical"
android:text="123) 5e2-5e3 1a1-1a3"
android:textColor="#000000"
android:textSize="11sp" />
</ScrollView>
</androidx.cardview.widget.CardView>
and in code:
-- in onCreate
tvMoveHistory = findViewById ( R.id.moveHistory )
svMoveHistory = findViewById ( R.id.svMoveHistory )
tvMoveHistory.movementMethod = ScrollingMovementMethod()
-- to actually add text
moveHistory.append ( newText )
-- during a central Refresh routine (yes, confirmed it runs via debugger)
svMoveHistory.post {
svMoveHistory.fullScroll(View.FOCUS_DOWN)
}
What's even more strange, I created a new project, minimal with just a few objects in order to re-create the issue.
It behaves perfectly whether I use append, or just straight assign it.
So I'm again baffled as to what's causing the issue ? (ie using append in my current project means no scroll to bottom, using .text = full text means scroll to bottom works).
However, re-testing in another fresh project results in expected behaviour?
Text I'm adding is very simple, no spannable string, no bold/html markup etc.
Just simple line in format of a simple chess-like notation:
12) a5-g6 e3-h7
... etc. (+ CR ie \n at end of line for new line)
I've scoured my logic, I literally don't touch that textView for any reason other than to append a small piece of text. Occassionally (ie new game), I reset it: = ""
but aside from above code, there is nothing else updating/modifying this textview/scrollview ?
Any ideas what I'm missing?