Strange Coolant Error Issue

Every afternoon, while on the way home from work, usually while traveling up a decent incline, I get a "Low Coolant Level" notice in the info screen. No chime sounds, not noise, but just the notice. It usually also then tells me the same thing when I turn off the car. I then check the level (Hot), and it is 2-3" above the cold full upper line.

I don't think I have ever gotten the message while driving to work in the morning.

I've been getting this message off and on for 4-5 months.

About 4 weeks ago, I noticed the level, when cold, was just above the bottom cold full line. So I purchased the correct coolant, and added some to raise it to the upper line.

I have heat, I don't overheat (temp gauge hasn't been noticeably different), but there is a faint smell of coolant when you open the hood. I have been religiously checking the level for these past 4 weeks, and it has barely changed. I assume from the smell that I have a leak somewhere, but it must be tiny. I haven't found any puddles of coolant anywhere.

I will be pulling the engine cover off and checking the thermostat housing area for leaks. Anywhere else I should be looking?

And why does the "Low Coolant" message pop up when I am not low on coolant?