Error while selecting tiles

Error while selecting tiles.
Some tiles are not selected while drawing lines or selecting tiles on the screen.
I am attaching the screen shot.
Can you please help me on that.

Hello.

If your programme’s system uses tiles duplicated in Prefab for drawing, the possible causes of the problem with some tiles not being selected are as follows.

-Slow processing speed and FPS
Is your FPS slow? Fast FPS and processing speed are essential conditions for running a project smoothly.

-The Collider’s judging is too small.
If a collider is used, is the collider set to the same shape as the size of the object?

-The correct hit detection (Collider) is not set.
If a collider is used to judge whether the object is touched by the mouse or not, the collider may not be set correctly if the shape of the collider is set incorrectly.

-Problems with the judgement script?
The simplest script to judge whether the mouse has touched the object is to use void OnMouseEnter().
A sample script is shown below.

void OnMouseEnter()
{
if(Input.GetMouseButton(0)) //Script to change the appearance.
}

At this time, if GetMouseButton is scripted to execute the specified script only at the moment it is pressed, like GetMouseButtonDown, it cannot be drawn smoothly like drawing lines with a pen.

These are the four possible causes of the problem. I am also a beginner, so there are limits to my capabilities. So if this is still difficult to solve, I recommend also using artificial intelligence such as Chat GPT or Bing AI.
(Due to the translation website, there may be some glitches in the text.)