You might have a little water getting in the valve stem. I had a similar problem on my Nissan Armada. Let about half the pressure out to blow the moisture out, then reinflate to the correct pressure. You might also want to try a new set of stem caps.
Noticed two things with my smart. If I happened to have the tires filled right up to the recommended pressure cold and drove a few days I would get the light blinking on so it seems to be sensitive to over pressure too. I used to use an analog gauge but switched to a digital which is part of the chuck that I use on my compressor and since switching to this setup I have not had issues with my light popping on vs the analog dial I was using.
The pencil type gauges are definitely not accurate.