Interesting; I just started my laptop to try some terminal commands for printing various information to potentially find something which could be related to the error. No luck.
However, I decided to run nvidia-settings again, but this time I used the recommended command from the bumblebee FAQ: ‘optirun -b none nvidia-settings -c :8’.
This was the first time i ran it with the ‘-b none’ parameter. To my amazement I could now see a changing clock frequency! I fired up Minecraft and it ran with good performance this time!
I then began to wonder if it was the extra parameter to nvidia-settings which had magically fixed it, or if it was the fact that I had run the laptop without having the AC-adapter connected to it (aka on battery). Putting the laptop in suspend mode, and then waking it, confirmed that I know have the same problem as weltensturm (the poster above) (the card was now stuck at 33 MHz). To fix it, I tried rebooting the computer, but the problem persisted across the reboot.
To fix it I have to shutdown the computer, disconnect the AC-adapter, and boot the computer while the AC-adapter remains disconnected. This seems to reset the card to a working state.
There is an option in /etc/bumblebee/bumblebee.conf which looks like this:
# Card power state at exit. Set to false if the card shoud be ON when Bumblebee
# server exits.
TurnCardOffAtExit=true
Perhaps something similar is needed, but specifically for suspend mode (even though I shutdown all applications which were started with ‘optirun’?)? Perhaps writing a script which does something similar?
Atleast now I can utilize the Nvidia GPU and know how to fix the problem when it appears!