First,

“Snap to Pixel Grid” is checked, but the object's position values ​​still appear as decimal points.
What's really unique is that the Y value only drops by 0.5 units.

Second,

When Rulers checked, Pixel Grid and the Ruler values did not match. 

Hi ​@yeon, Thanks for reaching out about this!

I understand you're experiencing an issue where objects are not snapping to the pixel grid, even with the Snap to Pixel Grid option enabled. 

Could you please provide more specific details about the behavior you're observing?

• Does this occur when you directly place a 48x48 object onto the canvas?  I've attempted to replicate this, but haven't been able to. If this is the case, please consider filing a bug report by following the instructions in this Help Center article: Submit a bug report
• Does this happen when you rotate an object?  If so, this behavior may be expected. Figma layers do not automatically snap to the pixel grid during rotation because the horizontal and vertical centers of the selection are used as the pivot point. You can find more details here: Adjust alignment, rotation, position, and dimensions
• Does this occur when you scale an object? If so, it might be related to the value you entered for the scale multiplier or the settings of the object’s anchor point. If applicable, reviewing your settings might be helpful: Scale layers while maintaining proportions  

For rotation and scaling, achieving precise grid alignment may require manually adjusting the layer's position.

If none of those scenarios fit what you're seeing, could you please give us a detailed breakdown of the steps to reproduce the issue?

And about the second issue you mentioned, it appears that the horizontal guides showing the same numbers as the Y position in the properties panel – could you explain what you were expecting to happen there?

We're looking forward to hearing back from you. If we need to, we'll get our support team involved for a closer look.

Note: It seems two similar topics were posted, so I've merged them here to improve their visibility.

Thank you!