Here's a recipe how to solve a particular problem with GNU Radio. More or less for my own record as I'm pretty sure I'll come across this same problem again on some other machine and it took some time to figure it out.
If suddenly GNU Radio instrumentation using the WX GUI (like FFT and waterfall plots) look all strange and broken like this:
the cause of the problem is that Python OpenGL bindings are not working for some reason. In this case GNU Radio will automatically fall back onto somewhat simpler widgets without any warnings in the console. These backup widgets however seem to be very outdated or downright broken. A lot of buttons and controls are missing and the waterfall plot is completely useless.
Package that needs to be installed on Debian is python-opengl.
After this is corrected, the same WX GUI FFT Sink as above will be shown like this:
You can override auto-detection of a working OpenGL installation by modifying the following part of etc/gnuradio/conf.d/gr-wxgui.conf. This is useful because if you force the style to gl you will actually see the error that is causing the code to fall back to non-GL widgets:
[wxgui] # 'gl', 'nongl', or 'auto' style = auto