There are actually 2 bugs in this thread:
1. The switching (or failure of it) between night and day mode
2. The flickering/blinking of the street names
The switching is a known bug and is being worked on by the Waze product team. We do not have any indication on when this will be fixed, but we will be informing everyone through the forums and the Facebook page when this is resolved. In the mean time, I prefer to use day mode, so I leave it on day mode permanently.
The blinking of the street names is actually a two-parter on its own.
There is a bug where the map/street names flicker. This bug is also known and is being worked on.
There is however also a feature on the map, that the labels of the streets switch when there is not enough space to display all the street names at the same time. So every 1 or 2 seconds, you see the labels switch between one and another set of labels. I don't know if this is a bug, or if this is by design, but I actually think it is extremely helpful because it doesn't allow for one street label to interfere with another, possibly making the map unreadable...