This is a strange one. I had the tyre, valve and seal checked over at my local tyre store. Nothing found.
Yesterday morning, -3c, tpms comes on. Pressure dropped to 0.5 bar.
I inflated the tyre to 2.2 bar.
This morning, -5c.....tyre still 2.2...no air lost.
I`ve been running around all morning, no pressure drop.
I recently purchased a wireless inflator from AliExpress. No cables. Xiaomi is the manufacturer.Slightly bigger and fatter than a mobile phone. It inflates my "flat" in around 8 minutes and still retains 2/3 of the battery power. Recharges by USB C.
Impressive gadget.