I am currently at Chapter 5 and had no problem with scroll speed until now.

I have no idea what exactly I touched but now even if I tap the arrow keys it will direct me to the edge of the map.
Mouse also behave similarly except it refuses to scroll down or right for some weird reason.

I have decreased the both mouth/keyboard scroll speed to min in the options but that didn't change anything.

Does anyone know how to fix this problem?

I checked whether the scroll key was causing the issue.

It was not.

However, I did find a partial solution. I wanted to check whether my previous save files were affected.
While my mouse scroll was not functioning, my keyboard scroll worked perfectly fine.

I am not sure what is causing the mouse scroll function to misbehaving, but at least now I can play the game without much discomfort.

The issue returns . . Reloading the save file no longer works now.

I have no idea what to do. It is extremely irritating to play the game as a result.
[rather than scrolling the map through arrow keys or mouse, I have to go to map, move the view, then return to the characters, move command, then go back to the map etc etc.]

Does anybody know how to fix this problem?

Go to ..\Documents\Baldur's Gate - Enhanced Edition\ and open 'baldur.lua' file in notepad (NOT Wordpad, or any other editor that formats). Look for the entries:

SetPrivateProfileString('Game Options','Keyboard Scroll Speed','XX')
SetPrivateProfileString('Game Options','Mouse Scroll Speed','XX')

Where 'XX' is the speed of scrolling. Mine is set quite high at 45.

I edited the value to 12 for both.

That fixed old save file with different character. However, it didn't fix my current character save files.
Welp . .

I might need to start the game over in order to fix this problem.

EDIT:

The bug only appears in Chapter 5 it seems. When I finished up everything and proceeded to the next area, the scroll speed became normal again.

It will be a chore to manually move the map everywhere, but it is only a temporary bug.