The blue dots are a prediction based on the 2 most recent readings using an auto-regressive second order model. If you see a lot of blue you might not be picking up sensor readings. More importanly, if you see more than a couple blue dots to the LEFT of the current time line, your data is stale.
Stale Data! This Nightscout rig has been offline since around 4AM.
If you unplugged your system to charge, or have other reasons to expect this, then all is well. If you are expecting the system to be online currently, then you need to start looking into it.