Front Right Tire Losing Air Rapidly – No Puncture Found, Need Advice

I have a Hyundai i20 Asta and am experiencing an issue with the front right tire.

About a month ago, all tires had 33 psi, but now, while the others are around 31 psi, the front right has dropped to 16 psi. I’ve noticed this tire loses air quickly, showing a visible difference within 15 days.

The puncture technician couldn’t find any puncture.
Any ideas on what could be causing this?
Can it be repaired, or will I need to replace the tire?