Nothing wrong with my keyboard.
I have also re-installed B4A, ADK, etc.. several times.
The symptoms of the 2 problems I have described (together with pictures and video) are very easy to reproduce.
For problem1, I am guessing there might be a fault in a background task in B4A Editor, the task could be the one that does dynamic reference look-up, syntax checking, etc. It doesn't like uppercase variable names. As I type, it could be trying to visually alert me around the cursor. Much like multiplexing LEDs to trick our eyes' persistent of vision, the display shows a composite of all the quick changes. So a text-based Editor can show graphic corruption like what I am seeing.
A clue:
Please look at the source codes
Sub Process_Globals
Dim Quantity as Int
End Sub
Sub abc (quantity as Int)
...
End Sub
As we go about editing our other parts of the source codes, we will notice that B4A Editor will eventually and autonomously change all occurrances of 'Quantity' to 'quantity'. B4A Editor does not like uppercase variable names.
For problem2, likely a bug in B4A Editor.