I think after I hit a small bump on the road over the weekend at 70mph and the TMPS sensor(red icon) on the dash came on soon.
After 20 minutes of driving to a safe place I was at 27psi on my passenger front tire. These tires only had 4k miles on them, got them at Discount Tires.

I inflate it on Sunday to 33psi cold and it is down to 26psi cold on Wednes, so I took it to different local tire repair shop to submerge it in water and we found no bubbles. There are no visible nails. It's strange as the TMPS came on more often every week now, instead of every few months of normal use.

I think it's a hole somewhere in the tire or the wheel that is not visible. I'll ask Discount Tires to inspect the individual tire and wheel separately for the leak source. Any other ideas? thanks