This is going to be an ever-evolving page, as I learn of common issues people identify when setting up the plugin.
Check you have a common ground between an external power supply, and the Pi. See more (including an example video) in the issue opened here
Make sure you have the correct order of RGB strip selected in the strip settings. You can use the LED Strip test to help debug this issue quickly.
Make sure you restart the OctoPrint server, and reload the web interface. You should see the wizard pop up, or the light/torch icon in the navbar.
It is likely that the OS level config is incorrect. To fix this, please head to the OS Configuration Test section (under 'Utilities') to run a test and fix the configuration. See the OS Configuration Test docs.
If you get the error:
ws2811_init failed with code -13 (Unable to initialize SPI)
plugin_ws281x_led_status_debug.log then it likely means that you have some extra peripherals attached to your Pi, that are taking up the SPI channels, therefore conflicting with the plugin's use of SPI.
A user reported that SPI failed to initialise with the above screen, however commenting out the lines the guide asked you to enter meant that both the screen and LEDs could work at the same time.
The dependency that this plugin relies on was not updated to add support for these boards as of the last release of the plugin. Please see this issue for instructions of how to fix it.
Some strips do not like 3.3V signals, and if you do use 3.3v (without a level shifter) then please keep the wires to the LEDs fairly short to avoid voltage drop.
Adding a 470Ω resistor in the signal line can help. Some guides recommend this, in my experience it is not always required. Worth a try if you have unstable signal to the LEDs. Link to issue.
Current theory behind this issue is bad power supply to the Raspberry Pi, which will create a throttled and unstable system. This can impact the precise timing the LEDs require and means they only display white.
To fix the issue, please use an adequate power supply with your Raspberry Pi. See the Raspberry Pi documentation for details on the specification for power supplies for different models.
Mixed reports that using a sacrificial LED on a short wire (to avoid voltage drop) can be beneficial for the LED strip. See this Hackaday article for more details. This solution is untested, only linked because it might be useful.