Most of the time I boot up and sound works fine, but less often when I boot into the system there is no sound and I have to reboot
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Are you dual-booting with Windows?
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Is the audio device missing after selecting ‘Restart’ from other OS, then booting to Manjaro?
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If ‘Shutdown’ is used to close other OS instead of ‘Restart’, is the audio device detected OK ?
If the answer to all 3 of those questions is yes, the problem is in Windows not Linux
the solution is to Turn Off Fast Startup in Windows 10
Windows does not technically reboot, It has a Fast Startup cheat feature that uses hybrid hibernation instead of full power-down, and appears to restart faster. Manjaro cannot initialise audio devices from hybrid hibernation, but rebooting Manjaro will clear the hybrid power state