It sounds like taking the tire pressure reading of the "problem tire (tyre)" manually, shows a constant slow leak in one tire. So the OP confirms it's "not a sensor issue".
I've had a similar problem. It was caused by a poorly sealed rim edge...either due to the tire or the rim itself. It was only confirmed by the process of elimination, since taking the tire off didn't reveal any puncture or air leaks and the valve stem wasn't leaking. The leaks seemed to happen under load, while the vehicle was moving. Try taking the tire off, then off the rim. Have them check for smoothness and any visible imperfections on the rim and tire inner edge. With the tire off the rim, clean and reseal the rim/tire edge then reinstall the tire. See if that works.
If not and it's still driving you crazy, consider swapping the problem tire with another good one on your vehicle, so swap tires by putting them on different rims, all from your vehicle. See if the problem remains with the same tire (in its new location...so you know it's the tire)...or the same rim (in the old location, so you know it's the rim). Hopefully in that fashion, you'll know if you need to replace the tire or rim. Wish I had an easier suggestion. Good luck!