It means you've reached the speed limit you've set in the CA's setup menus.
If you use the left button once to get to the diagnostic screen, you'll see a capital S during those times, and a lowercase s the rest of the time.
I recommend reading up on the Grin Tech CA3 product info page, which describes the various menus and setup options, and what they do, as well as the various screens the CA has and what info is displayed on each one. The CA3 manual is also there, and it explains the various limiting features as well.
Then you can setup the various limits to do what you want, or turn them off (where applicable) for things you don't want limited.
Unless you are using it only for monitoring, and do not have it's throttle output connected to your controller(s), then if you don't read the manual, and go thru the whole CA3 setup menu set, completely, to ensure it's all setup the way your system needs it to be set to make it operate like you want, you may get unexpected and undesirable and possibly even what will seem like "unpredictable" behavior from your system, potentially at the worst possible time.
It's a complex device, with a lot of interactions between various settings. :/