Soon after starting our 2015 Prius C I noticed on the screen that there was a "progress" indicator showing what I took to be a download but was perhaps something reloading from within. If there was info attached before it started, I wasn't looking so no help there, and the screen simply opened up after the 30 second or so process. In case it matters, miles are around 33,000 and the car had been sitting idle for a couple weeks (certainly not for the first time). Any ideas?
I don't think so but can't say for certain. One possibility I suppose is a map update (via satellite?), but I was of the impression anyway that these are done with a new chip (if or when offered). But I am less than certain of that as well. I suppose another possibility is via Bluetooth...unless, again, it is some kind of re-boot.
I don't know about other versions in other regions but the USA-delivered c never had anything in it that could be updated without a wired link, and precious few things that could be written to even with a wired link.
No need to jump, no replaced 12v battery, and no other issues that were obvious, nor any changes in screen info that I could detect in a short drive. In other words essentially no noticeable changes nor any unusual (or usual, for that matter) service or operations between drives.
On my 2010, if there has been any actual interruption of power, such as a dead battery, the MFD will reboot the next time the car's powered on. It looks about like that, there's a progress bar on the screen. Normally it just goes into a sleep mode when the car is turned off, so it doesn't have to boot every time the car starts. I wonder if for your year/model they included a time limit of N days for the sleep mode, and then it really turns off to save battery, and then it reboots when you start the car next time. Just a guess.
A plausible guess, though I would have expected to notice it on other occasions that left the car unused that long. But it was pretty quick and possible, perhaps, to miss.